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90-488: Elements of biosynthesis include: precursor compounds, chemical energy (e.g. ATP ), and catalytic enzymes which may need coenzymes (e.g. NADH , NADPH ). These elements create monomers , the building blocks for macromolecules. Some important biological macromolecules include: proteins , which are composed of amino acid monomers joined via peptide bonds , and DNA molecules, which are composed of nucleotides joined via phosphodiester bonds . Biosynthesis occurs due to

180-505: A bilayer structure of phospholipids. The phospholipid molecule is amphipathic ; it contains a hydrophilic polar head and a hydrophobic nonpolar tail. The phospholipid heads interact with each other and aqueous media, while the hydrocarbon tails orient themselves in the center, away from water. These latter interactions drive the bilayer structure that acts as a barrier for ions and molecules. There are various types of phospholipids; consequently, their synthesis pathways differ. However,

270-429: A carboxyl group "head" and a hydrocarbon chain "tail". These fatty acids create larger components, which in turn incorporate noncovalent interactions to form the lipid bilayer. Fatty acid chains are found in two major components of membrane lipids: phospholipids and sphingolipids . A third major membrane component, cholesterol , does not contain these fatty acid units. The foundation of all biomembranes consists of

360-784: A flavin group , which may be in the form of FAD or flavin mononucleotide (FMN). Many flavoproteins are known: components of the succinate dehydrogenase complex, α-ketoglutarate dehydrogenase , and a component of the pyruvate dehydrogenase complex . FAD can exist in four redox states, which are the flavin-N(5)-oxide , quinone , semiquinone , and hydroquinone . FAD is converted between these states by accepting or donating electrons. FAD, in its fully oxidized form, or quinone form, accepts two electrons and two protons to become FADH 2 (hydroquinone form). The semiquinone (FADH ) can be formed by either reduction of FAD or oxidation of FADH 2 by accepting or donating one electron and one proton, respectively. Some proteins, however, generate and maintain

450-427: A glycosidic bond , the flavin mononucleotide is not truly a nucleotide. This makes the dinucleotide name misleading; however, the flavin mononucleotide group is still very close to a nucleotide in its structure and chemical properties. FAD can be reduced to FADH 2 through the addition of 2 H and 2 e . FADH 2 can also be oxidized by the loss of 1 H and 1 e to form FADH. The FAD form can be recreated through

540-619: A precursor is a compound that participates in a chemical reaction that produces another compound. In biochemistry , the term "precursor" often refers more specifically to a chemical compound preceding another in a metabolic pathway , such as a protein precursor . In 1988, the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances introduced detailed provisions and requirements relating

630-469: A primer with a free 3'OH in which to incorporate nucleotides. In order for DNA replication to occur, a replication fork is created by enzymes called helicases which unwind the DNA helix. Topoisomerases at the replication fork remove supercoils caused by DNA unwinding, and single-stranded DNA binding proteins maintain the two single-stranded DNA templates stabilized prior to replication. DNA synthesis

720-453: A purine or pyrimidine base with a glycosidic bond and a phosphate group at the 5' location of the sugar. The DNA nucleotides adenosine and guanosine consist of a purine base attached to a ribose sugar with a glycosidic bond. In the case of RNA nucleotides deoxyadenosine and deoxyguanosine , the purine bases are attached to a deoxyribose sugar with a glycosidic bond. The purine bases on DNA and RNA nucleotides are synthesized in

810-445: A charged tRNA that is ready to add amino acids to the growing polypeptide chain. In addition to binding an amino acid, tRNA has a three nucleotide unit called an anticodon that base pairs with specific nucleotide triplets on the mRNA called codons ; codons encode a specific amino acid. This interaction is possible thanks to the ribosome, which serves as the site for protein synthesis. The ribosome possesses three tRNA binding sites:

900-446: A class of molecules called sterols . Sterols have four fused rings and a hydroxyl group . Cholesterol is a particularly important molecule. Not only does it serve as a component of lipid membranes, it is also a precursor to several steroid hormones, including cortisol , testosterone , and estrogen . Cholesterol is synthesized from acetyl CoA . The pathway is shown below: More generally, this synthesis occurs in three stages, with

990-517: A more positive reduction potential than NAD+ and is a very strong oxidizing agent. The cell utilizes this in many energetically difficult oxidation reactions such as dehydrogenation of a C-C bond to an alkene . FAD-dependent proteins function in a large variety of metabolic pathways including electron transport, DNA repair, nucleotide biosynthesis, beta-oxidation of fatty acids, amino acid catabolism, as well as synthesis of other cofactors such as CoA , CoQ and heme groups. One well-known reaction

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1080-620: A non-invasive manner. The field has advanced in recent years with a number of new tools, including those to trigger light sensitivity, such as the Blue-Light-Utilizing FAD domains (BLUF). BLUFs encode a 100 to 140 amino acid sequence that was derived from photoreceptors in plants and bacteria. Similar to other photoreceptors , the light causes structural changes in the BLUF domain that results in disruption of downstream interactions. Current research investigates proteins with

1170-454: A polar head and nonpolar tails. Unlike phospholipids, sphingolipids have a sphingosine backbone. Sphingolipids exist in eukaryotic cells and are particularly abundant in the central nervous system . For example, sphingomyelin is part of the myelin sheath of nerve fibers. Sphingolipids are formed from ceramides that consist of a fatty acid chain attached to the amino group of a sphingosine backbone. These ceramides are synthesized from

1260-625: A process called translation . During translation, genetic material called mRNA is read by ribosomes to generate a protein polypeptide chain. This process requires transfer RNA (tRNA) which serves as an adaptor by binding amino acids on one end and interacting with mRNA at the other end; the latter pairing between the tRNA and mRNA ensures that the correct amino acid is added to the chain. Protein synthesis occurs in three phases: initiation, elongation, and termination. Prokaryotic ( archaeal and bacterial ) translation differs from eukaryotic translation ; however, this section will mostly focus on

1350-471: A prosthetic group, this prosthetic group can be tightly bound or covalently linked. Only about 5-10% of flavoproteins have a covalently linked FAD, but these enzymes have stronger redox power. In some instances, FAD can provide structural support for active sites or provide stabilization of intermediates during catalysis. Based on the available structural data, the known FAD-binding sites can be divided into more than 200 types. 90 flavoproteins are encoded in

1440-469: A reaction using a carbon radical. FAD plays a major role as an enzyme cofactor along with flavin mononucleotide , another molecule originating from riboflavin. Bacteria, fungi and plants can produce riboflavin , but other eukaryotes , such as humans, have lost the ability to make it. Therefore, humans must obtain riboflavin, also known as vitamin B2, from dietary sources. Riboflavin is generally ingested in

1530-503: A series of chemical reactions. For these reactions to take place, the following elements are necessary: In the simplest sense, the reactions that occur in biosynthesis have the following format: Some variations of this basic equation which will be discussed later in more detail are: Many intricate macromolecules are synthesized in a pattern of simple, repeated structures. For example, the simplest structures of lipids are fatty acids . Fatty acids are hydrocarbon derivatives; they contain

1620-477: A similar manner but do not permit protein function could be useful mechanisms of inhibiting bacterial infection. Alternatively, drugs blocking FAD synthesis could achieve the same goal; this is especially intriguing because human and bacterial FAD synthesis relies on very different enzymes, meaning that a drug made to target bacterial FAD synthase would be unlikely to interfere with the human FAD synthase enzymes. Optogenetics allows control of biological events in

1710-558: A substrate analogue, which suggests that it is short-lived. However, when using a fluorinated substrate, a neutral flavin semiquinone was detected. Glutamate synthase catalyzes the conversion of 2-oxoglutarate into L-glutamate with L-glutamine serving as the nitrogen source for the reaction. All glutamate syntheses are iron-sulfur flavoproteins containing an iron-sulfur cluster and FMN. The three classes of glutamate syntheses are categorized based on their sequences and biochemical properties. Even though there are three classes of this enzyme, it

1800-408: A superoxidized form of the flavin cofactor, the flavin-N(5)-oxide. Flavoproteins were first discovered in 1879 by separating components of cow's milk. They were initially called lactochrome due to their milky origin and yellow pigment . It took 50 years for the scientific community to make any substantial progress in identifying the molecules responsible for the yellow pigment. The 1930s launched

1890-492: A twelve-step reaction mechanism present in most single-celled organisms. Higher eukaryotes employ a similar reaction mechanism in ten reaction steps. Purine bases are synthesized by converting phosphoribosyl pyrophosphate (PRPP) to inosine monophosphate (IMP), which is the first key intermediate in purine base biosynthesis. Further enzymatic modification of IMP produces the adenosine and guanosine bases of nucleotides. Other DNA and RNA nucleotide bases that are linked to

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1980-410: Is a two-step reaction which involves the conversion of UMP to UTP . Phosphate addition to UMP is catalyzed by a kinase enzyme. The enzyme CTP synthase catalyzes the next reaction step: the conversion of UTP to CTP by transferring an amino group from glutamine to uridine; this forms the cytosine base of CTP. The mechanism, which depicts the reaction UTP + ATP + glutamine ⇔ CTP + ADP + glutamate,

2070-562: Is believed that they all operate through the same mechanism, only differing by what first reduces the FMN. The enzyme produces two glutamate molecules: one by the hydrolysis of glutamine (forming glutamate and ammonia), and the second by the ammonia produced from the first reaction attacking 2-oxoglutarate, which is reduced by FMN to glutamate. Due to the importance of flavoproteins , it is unsurprising that approximately 60% of human flavoproteins cause human disease when mutated. In some cases, this

2160-450: Is below: Cytosine is a nucleotide that is present in both DNA and RNA. However, uracil is only found in RNA. Therefore, after UTP is synthesized, it is must be converted into a deoxy form to be incorporated into DNA. This conversion involves the enzyme ribonucleoside triphosphate reductase . This reaction that removes the 2'-OH of the ribose sugar to generate deoxyribose is not affected by

2250-405: Is bound to a cyclic ribose at the 1' carbon, while phosphate is bound to the ribose at the 5' carbon to form the adenine nucledotide. Riboflavin is formed by a carbon-nitrogen (C-N) bond between the isoalloxazine and the ribitol . The phosphate group is then bound to the terminal ribose carbon, forming a FMN. Because the bond between the isoalloxazine and the ribitol is not considered to be

2340-441: Is catalyzed by the enzyme phosphoserine phosphatase , which dephosphorylates L-phosphoserine to yield L-serine . There are two known pathways for the biosynthesis of glycine. Organisms that use ethanol and acetate as the major carbon source utilize the glyconeogenic pathway to synthesize glycine . The other pathway of glycine biosynthesis is known as the glycolytic pathway. This pathway converts serine synthesized from

2430-402: Is catalyzed by the enzyme pyrroline-5-carboxylate synthase (P5CS), which catalyzes the reduction of the ϒ-carboxyl group of L-glutamate 5-phosphate. This results in the formation of glutamate semialdehyde, which spontaneously cyclizes to pyrroline-5-carboxylate. Pyrroline-5-carboxylate is further reduced by the enzyme pyrroline-5-carboxylate reductase (P5CR) to yield a proline amino acid. In

2520-408: Is composed of nucleotides that are joined by phosphodiester bonds . DNA synthesis , which takes place in the nucleus , is a semiconservative process, which means that the resulting DNA molecule contains an original strand from the parent structure and a new strand. DNA synthesis is catalyzed by a family of DNA polymerases that require four deoxynucleoside triphosphates, a template strand , and

2610-410: Is converted to phosphatidate via the addition of another fatty acid chain contributed by a second acyl CoA; all of these steps are catalyzed by the glycerol phosphate acyltransferase enzyme. Phospholipid synthesis continues in the endoplasmic reticulum, and the biosynthesis pathway diverges depending on the components of the particular phospholipid. Like phospholipids, these fatty acid derivatives have

2700-759: Is due to a decreased affinity for FAD or FMN and so excess riboflavin intake may lessen disease symptoms, such as for multiple acyl-CoA dehydrogenase deficiency . In addition, riboflavin deficiency itself (and the resulting lack of FAD and FMN) can cause health issues. For example, in ALS patients, there are decreased levels of FAD synthesis. Both of these paths can result in a variety of symptoms, including developmental or gastrointestinal abnormalities, faulty fat break-down , anemia , neurological problems, cancer or heart disease , migraine , worsened vision and skin lesions. The pharmaceutical industry therefore produces riboflavin to supplement diet in certain cases. In 2008,

2790-495: Is highly conserved to maintain precisely the alignment of electron donor NADPH and acceptor FAD for efficient electron transfer. The two electrons in reduced FAD are transferred one a time to adrenodoxin which in turn donates the single electron to the heme group of the mitochondrial P450. The structures of the reductase of the microsomal versus reductase of the mitochondrial P450 systems are completely different and show no homology. p -Hydroxybenzoate hydroxylase (PHBH) catalyzes

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2880-447: Is initiated by the RNA polymerase primase , which makes an RNA primer with a free 3'OH. This primer is attached to the single-stranded DNA template, and DNA polymerase elongates the chain by incorporating nucleotides; DNA polymerase also proofreads the newly synthesized DNA strand. During the polymerization reaction catalyzed by DNA polymerase, a nucleophilic attack occurs by the 3'OH of

2970-449: Is less generally accepted because no spectral or electron paramagnetic resonance evidence exists for the presence of a radical intermediate. The nucleophilic mechanism is more favored because it is supported by site-directed mutagenesis studies which mutated two tyrosine residues that were expected to increase the nucleophilicity of the substrates. Glucose oxidase (GOX) catalyzes the oxidation of β-D-glucose to D-glucono-δ-lactone with

3060-549: Is made discontinuously in Okazaki fragments and grows away from the replication fork. Okazaki fragments are covalently joined by DNA ligase to form a continuous strand. Then, to complete DNA replication, RNA primers are removed, and the resulting gaps are replaced with DNA and joined via DNA ligase. A protein is a polymer that is composed from amino acids that are linked by peptide bonds . There are more than 300 amino acids found in nature of which only twenty two, known as

3150-564: Is observed at 450 nm, with an extinction coefficient of 11,300 M cm . Flavins in general have fluorescent activity when unbound (proteins bound to flavin nucleic acid derivatives are called flavoproteins ). This property can be utilized when examining protein binding, observing loss of fluorescent activity when put into the bound state. Oxidized flavins have high absorbances of about 450 nm, and fluoresce at about 515-520 nm. In biological systems, FAD acts as an acceptor of H and e in its fully oxidized form, an acceptor or donor in

3240-524: Is part of the citric acid cycle (also known as the TCA or Krebs cycle); succinate dehydrogenase (complex II in the electron transport chain ) requires covalently bound FAD to catalyze the oxidation of succinate to fumarate by coupling it with the reduction of ubiquinone to ubiquinol . The high-energy electrons from this oxidation are stored momentarily by reducing FAD to FADH 2 . FADH 2 then reverts to FAD, sending its two high-energy electrons through

3330-468: Is responsible for synthesizing thymine residues from dUMP to dTMP . This reaction transfers a methyl group onto the uracil base of dUMP to generate dTMP. The thymidylate synthase reaction, dUMP + 5,10-methylenetetrahydrofolate ⇔ dTMP + dihydrofolate, is shown to the right. Although there are differences between eukaryotic and prokaryotic DNA synthesis, the following section denotes key characteristics of DNA replication shared by both organisms. DNA

3420-429: Is synthesized by an ATP-dependent addition of an amino group onto aspartate; asparagine synthetase catalyzes the addition of nitrogen from glutamine or soluble ammonia to aspartate to yield asparagine. The diaminopimelic acid biosynthetic pathway of lysine belongs to the aspartate family of amino acids. This pathway involves nine enzyme-catalyzed reactions that convert aspartate to lysine. Protein synthesis occurs via

3510-421: Is vital for bacterial virulence, and so targeting FAD synthesis or creating FAD analogs could be a useful area of investigation. Already, scientists have determined the two structures FAD usually assumes once bound: either an extended or a butterfly conformation, in which the molecule essentially folds in half, resulting in the stacking of the adenine and isoalloxazine rings. FAD imitators that are able to bind in

3600-472: The NADPH -dependent reduction of enolpyruvyl-UDP-N-acetylglucosamine (substrate) to the corresponding D-lactyl compound UDP-N-acetylmuramic acid (product). MurB is a monomer and contains one FAD molecule. Before the substrate can be converted to product, NADPH must first reduce FAD. Once NADP dissociates, the substrate can bind and the reduced flavin can reduce the product. Glutathione reductase (GR) catalyzes

3690-417: The acylation of sphingosine. The biosynthetic pathway for sphingosine is found below: As the image denotes, during sphingosine synthesis, palmitoyl CoA and serine undergo a condensation reaction which results in the formation of 3-dehydrosphinganine. This product is then reduced to form dihydrospingosine, which is converted to sphingosine via the oxidation reaction by FAD . This lipid belongs to

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3780-413: The catabolism of norepinephrine , serotonin and dopamine . MAO oxidizes primary, secondary and tertiary amines, which nonenzymatically hydrolyze from the imine to aldehyde or ketone . Even though this class of enzyme has been extensively studied, its mechanism of action is still being debated. Two mechanisms have been proposed: a radical mechanism and a nucleophilic mechanism. The radical mechanism

3870-435: The cytosol and mitochondria . It seems that FAD is synthesized in both locations and potentially transported where needed. Flavoproteins utilize the unique and versatile structure of flavin moieties to catalyze difficult redox reactions. Since flavins have multiple redox states they can participate in processes that involve the transfer of either one or two electrons, hydrogen atoms, or hydronium ions. The N5 and C4a of

3960-517: The proteinogenic amino acids , are the building blocks for protein. Only green plants and most microbes are able to synthesize all of the 20 standard amino acids that are needed by all living species. Mammals can only synthesize ten of the twenty standard amino acids. The other amino acids, valine , methionine , leucine , isoleucine , phenylalanine , lysine , threonine and tryptophan for adults and histidine , and arginine for babies are obtained through diet. The general structure of

4050-526: The FADH form, and a donor in the reduced FADH 2 form. The diagram below summarizes the potential changes that it can undergo. Along with what is seen above, other reactive forms of FAD can be formed and consumed. These reactions involve the transfer of electrons and the making/breaking of chemical bonds . Through reaction mechanisms , FAD is able to contribute to chemical activities within biological systems. The following pictures depict general forms of some of

4140-481: The N-acetyl-L-ornithine. The acetyl group of acetylornithine is removed by the enzyme acetylornithinase (AO) or ornithine acetyltransferase (OAT), and this yields ornithine . Then, the enzymes citrulline and argininosuccinate convert ornithine to arginine. There are two distinct lysine biosynthetic pathways: the diaminopimelic acid pathway and the α-aminoadipate pathway . The most common of

4230-607: The P450. The P450 systems that are located in the mitochondria are dependent on two electron transfer proteins: An FAD containing adrenodoxin reductase (AR) and a small iron-sulfur group containing protein named adrenodoxin . FAD is embedded in the FAD-binding domain of AR. The FAD of AR is reduced to FADH 2 by transfer of two electrons from NADPH that binds in the NADP-binding domain of AR. The structure of this enzyme

4320-415: The actions that FAD can be involved in. Mechanisms 1 and 2 represent hydride gain, in which the molecule gains what amounts to be one hydride ion. Mechanisms 3 and 4 radical formation and hydride loss. Radical species contain unpaired electron atoms and are very chemically active. Hydride loss is the inverse process of the hydride gain seen before. The final two mechanisms show nucleophilic addition and

4410-413: The amino acid lysine , which is derived from α-ketoglutarate . The biosynthesis of glutamate and glutamine is a key step in the nitrogen assimilation discussed above. The enzymes GOGAT and GDH catalyze the nitrogen assimilation reactions. In bacteria, the enzyme glutamate 5-kinase initiates the biosynthesis of proline by transferring a phosphate group from ATP onto glutamate. The next reaction

4500-544: The aminoacyl site (A site), the peptidyl site (P site), and the exit site (E site). There are numerous codons within an mRNA transcript, and it is very common for an amino acid to be specified by more than one codon; this phenomenon is called degeneracy . In all, there are 64 codons, 61 of each code for one of the 20 amino acids, while the remaining codons specify chain termination. As previously mentioned, translation occurs in three phases: initiation, elongation, and termination. Precursor (chemistry) In chemistry ,

4590-400: The appended BLUF domain and how different external factors can impact the proteins. There are a number of molecules in the body that have native fluorescence including tryptophan, collagen , FAD, NADH and porphyrins . Scientists have taken advantage of this by using them to monitor disease progression or treatment effectiveness or aid in diagnosis. For instance, native fluorescence of

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4680-484: The aromatic structure provides. FADH 2 is an energy-carrying molecule, because, once oxidized it regains aromaticity and releases the energy represented by this stabilization. The spectroscopic properties of FAD and its variants allows for reaction monitoring by use of UV-VIS absorption and fluorescence spectroscopies. Each form of FAD has distinct absorbance spectra, making for easy observation of changes in oxidation state. A major local absorbance maximum for FAD

4770-497: The aspartate family even though part of their carbon skeleton is derived from pyruvate . In the case of methionine, the methyl carbon is derived from serine and the sulfur group, but in most organisms, it is derived from cysteine. The biosynthesis of aspartate is a one step reaction that is catalyzed by a single enzyme. The enzyme aspartate aminotransferase catalyzes the transfer of an amino group from aspartate onto α-ketoglutarate to yield glutamate and oxaloacetate . Asparagine

4860-454: The bases attached to the sugar. This non-specificity allows ribonucleoside triphosphate reductase to convert all nucleotide triphosphates to deoxyribonucleotide by a similar mechanism. In contrast to uracil, thymine bases are found mostly in DNA, not RNA. Cells do not normally contain thymine bases that are linked to ribose sugars in RNA, thus indicating that cells only synthesize deoxyribose-linked thymine. The enzyme thymidylate synthetase

4950-457: The carbons needed for the biosynthesis of the methionine and histidine . During serine biosynthesis, the enzyme phosphoglycerate dehydrogenase catalyzes the initial reaction that oxidizes 3-phospho-D-glycerate to yield 3-phosphonooxypyruvate . The following reaction is catalyzed by the enzyme phosphoserine aminotransferase , which transfers an amino group from glutamate onto 3-phosphonooxypyruvate to yield L-phosphoserine . The final step

5040-406: The commonalities between the two organisms. Before translation can begin, the process of binding a specific amino acid to its corresponding tRNA must occur. This reaction, called tRNA charging, is catalyzed by aminoacyl tRNA synthetase . A specific tRNA synthetase is responsible for recognizing and charging a particular amino acid. Furthermore, this enzyme has special discriminator regions to ensure

5130-634: The control of precursors used to produce drugs of abuse. In Europe the Regulation (EC) No. 273/2004 of the European Parliament and of the Council on drug precursors was adopted on 11 February 2004. ( European law on drug precursors ) On January 15, 2013, the Regulation (EU) No. 98/2013 of the European Parliament and of the Council on the marketing and use of explosives precursors was adopted. The Regulation harmonises rules across Europe on

5220-408: The correct binding between tRNA and its cognate amino acid. The first step for joining an amino acid to its corresponding tRNA is the formation of aminoacyl-AMP: This is followed by the transfer of the aminoacyl group from aminoacyl-AMP to a tRNA molecule. The resulting molecule is aminoacyl-tRNA : The combination of these two steps, both of which are catalyzed by aminoacyl tRNA synthetase, produces

5310-424: The discovery of flavins paved the way for many scientists in the 40s and 50s to discover copious amounts of redox biochemistry and link them together in pathways such as the citric acid cycle and ATP synthesis. Flavin adenine dinucleotide consists of two portions: the adenine nucleotide ( adenosine monophosphate ) and the flavin mononucleotide (FMN) bridged together through their phosphate groups. Adenine

5400-1004: The electron transport chain; the energy in FADH 2 is enough to produce 1.5 equivalents of ATP by oxidative phosphorylation . Some redox flavoproteins non-covalently bind to FAD like Acetyl-CoA-dehydrogenases which are involved in beta-oxidation of fatty acids and catabolism of amino acids like leucine ( isovaleryl-CoA dehydrogenase ), isoleucine , (short/branched-chain acyl-CoA dehydrogenase), valine (isobutyryl-CoA dehydrogenase), and lysine ( glutaryl-CoA dehydrogenase ). Additional examples of FAD-dependent enzymes that regulate metabolism are glycerol-3-phosphate dehydrogenase (triglyceride synthesis) and xanthine oxidase involved in purine nucleotide catabolism. Noncatalytic functions that FAD can play in flavoproteins include as structural roles, or involved in blue-sensitive light photoreceptors that regulate biological clocks and development, generation of light in bioluminescent bacteria. Flavoproteins have either an FMN or FAD molecule as

5490-416: The environment could contribute to an early location of sites where illegal substances (both explosives and drugs of abuse) are produced. Flavin adenine dinucleotide In biochemistry , flavin adenine dinucleotide ( FAD ) is a redox -active coenzyme associated with various proteins , which is involved with several enzymatic reactions in metabolism . A flavoprotein is a protein that contains

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5580-473: The enzyme glutamate dehydrogenase (GDH). GDH is able to transfer ammonia onto 2-oxoglutarate and form glutamate. Furthermore, the enzyme glutamine synthetase (GS) is able to transfer ammonia onto glutamate and synthesize glutamine, replenishing glutamine. The glutamate family of amino acids includes the amino acids that derive from the amino acid glutamate. This family includes: glutamate, glutamine , proline , and arginine . This family also includes

5670-409: The enzyme glutamine oxoglutarate aminotransferase (GOGAT) which removes the amide amino group of glutamine and transfers it onto 2-oxoglutarate , producing two glutamate molecules. In this catalysis reaction, glutamine serves as the nitrogen source. An image illustrating this reaction is found to the right. The other pathway for incorporating nitrogen onto the α-carbon of amino acids involves

5760-466: The enzyme serine acetyltransferase catalyzes the transfer of acetyl group from acetyl-CoA onto L-serine to yield O-acetyl-L-serine . The following reaction step, catalyzed by the enzyme O-acetyl serine (thiol) lyase , replaces the acetyl group of O-acetyl-L-serine with sulfide to yield cysteine. The aspartate family of amino acids includes: threonine , lysine , methionine , isoleucine , and aspartate. Lysine and isoleucine are considered part of

5850-478: The enzyme nor the pigment was capable of oxidizing NADH on their own, but mixing them together would restore activity. Theorell confirmed the pigment to be riboflavin 's phosphate ester, flavin mononucleotide (FMN) in 1937, which was the first direct evidence for enzyme cofactors . Warburg and Christian then found FAD to be a cofactor of D-amino acid oxidase through similar experiments in 1938. Warburg's work with linking nicotinamide to hydride transfers and

5940-421: The field of coenzyme research with the publication of many flavin and nicotinamide derivative structures and their obligate roles in redox catalysis. German scientists Otto Warburg and Walter Christian discovered a yeast derived yellow protein required for cellular respiration in 1932. Their colleague Hugo Theorell separated this yellow enzyme into apoenzyme and yellow pigment, and showed that neither

6030-472: The first stage taking place in the cytoplasm and the second and third stages occurring in the endoplasmic reticulum. The stages are as follows: The biosynthesis of nucleotides involves enzyme- catalyzed reactions that convert substrates into more complex products. Nucleotides are the building blocks of DNA and RNA . Nucleotides are composed of a five-membered ring formed from ribose sugar in RNA, and deoxyribose sugar in DNA; these sugars are linked to

6120-407: The first step in phospholipid synthesis involves the formation of phosphatidate or diacylglycerol 3-phosphate at the endoplasmic reticulum and outer mitochondrial membrane . The synthesis pathway is found below: The pathway starts with glycerol 3-phosphate, which gets converted to lysophosphatidate via the addition of a fatty acid chain provided by acyl coenzyme A . Then, lysophosphatidate

6210-555: The first step of arginine biosynthesis in bacteria, glutamate is acetylated by transferring the acetyl group from acetyl-CoA at the N-α position; this prevents spontaneous cyclization. The enzyme N-acetylglutamate synthase (glutamate N-acetyltransferase) is responsible for catalyzing the acetylation step. Subsequent steps are catalyzed by the enzymes N-acetylglutamate kinase , N-acetyl-gamma-glutamyl-phosphate reductase , and acetylornithine/succinyldiamino pimelate aminotransferase and yield

6300-438: The form can have a large impact on other chemical properties. For example, FAD, the fully oxidized form is subject to nucleophilic attack , the fully reduced form, FADH 2 has high polarizability , while the half reduced form is unstable in aqueous solution. FAD is an aromatic ring system, whereas FADH 2 is not. This means that FADH 2 is significantly higher in energy, without the stabilization through resonance that

6390-407: The fully oxidized flavin ring are also susceptible to nucleophilic attack . This wide variety of ionization and modification of the flavin moiety can be attributed to the isoalloxazine ring system and the ability of flavoproteins to drastically perturb the kinetic parameters of flavins upon binding, including flavin adenine dinucleotide (FAD). The number of flavin-dependent protein encoded genes in

6480-411: The further loss of 1 H and 1 e . FAD formation can also occur through the reduction and dehydration of flavin-N(5)-oxide. Based on the oxidation state, flavins take specific colors when in aqueous solution . flavin-N(5)-oxide (superoxidized) is yellow-orange, FAD (fully oxidized) is yellow, FADH (half reduced) is either blue or red based on the pH , and the fully reduced form is colorless. Changing

6570-483: The genome (the flavoproteome) is species dependent and can range from 0.1% - 3.5%, with humans having 90 flavoprotein encoded genes. FAD is the more complex and abundant form of flavin and is reported to bind to 75% of the total flavoproteome and 84% of human encoded flavoproteins. Cellular concentrations of free or non-covalently bound flavins in a variety of cultured mammalian cell lines were reported for FAD (2.2-17.0 amol/cell) and FMN (0.46-3.4 amol/cell). FAD has

6660-494: The global need for riboflavin was 6,000 tons per year, with production capacity of 10,000 tons. This $ 150 to 500 million market is not only for medical applications, but is also used as a supplement to animal food in the agricultural industry and as a food colorant . New design of anti-bacterial medications is of continuing importance in scientific research as bacterial antibiotic resistance to common antibiotics increases. A specific metabolic protein that uses FAD ( Complex II )

6750-399: The growing chain on the innermost phosphorus atom of a deoxynucleoside triphosphate; this yields the formation of a phosphodiester bridge that attaches a new nucleotide and releases pyrophosphate . Two types of strands are created simultaneously during replication: the leading strand , which is synthesized continuously and grows towards the replication fork, and the lagging strand , which

6840-430: The human genome; about 84% require FAD, and around 16% require FMN, whereas 5 proteins require both to be present. Flavoproteins are mainly located in the mitochondria because of their redox power. Of all flavoproteins, 90% perform redox reactions and the other 10% are transferases , lyases , isomerases , ligases . Monoamine oxidase (MAO) is an extensively studied flavoenzyme due to its biological importance with

6930-418: The intermediates of glycolysis to glycine. In the glycolytic pathway, the enzyme serine hydroxymethyltransferase catalyzes the cleavage of serine to yield glycine and transfers the cleaved carbon group of serine onto tetrahydrofolate , forming 5,10-methylene-tetrahydrofolate . Cysteine biosynthesis is a two-step reaction that involves the incorporation of inorganic sulfur . In microorganisms and plants,

7020-522: The making available, introduction, possession and use, of certain substances or mixtures that could be misused for the illicit manufacture of explosives. A portable, advanced sensor based on infrared spectroscopy in a hollow fiber matched to a silicon-micromachined fast gas chromatography column can analyze illegal stimulants and precursors with nanogram-level sensitivity. Raman spectroscopy has been successfully tested to detect explosives and their precursors. Technologies able to detect precursors in

7110-401: The neutral and anionic semiquinones are observed which indicates a radical mechanism. Prenylcysteine lyase (PCLase) catalyzes the cleavage of prenylcysteine (a protein modification) to form an isoprenoid aldehyde and the freed cysteine residue on the protein target. The FAD is non-covalently bound to PCLase. Not many mechanistic studies have been done looking at the reactions of the flavin, but

7200-524: The oxygenation of p -hydroxybenzoate ( p OHB) to 3,4-dihyroxybenzoate (3,4-diOHB); FAD, NADPH and molecular oxygen are all required for this reaction. NADPH first transfers a hydride equivalent to FAD, creating FADH , and then NADP dissociates from the enzyme. Reduced PHBH then reacts with molecular oxygen to form the flavin-C(4a)-hydroperoxide. The flavin hydroperoxide quickly hydroxylates p OHB, and then eliminates water to regenerate oxidized flavin. An alternative flavin-mediated oxygenation mechanism involves

7290-452: The proposed mechanism is shown below. A hydride transfer from the C1 of the prenyl moiety to FAD is proposed, resulting in the reduction of the flavin to FADH 2 . COformED IS a carbocation that is stabilized by the neighboring sulfur atom. FADH 2 then reacts with molecular oxygen to restore the oxidized enzyme. UDP-N-acetylenolpyruvylglucosamine Reductase (MurB) is an enzyme that catalyzes

7380-536: The reduction of glutathione disulfide (GSSG) to glutathione (GSH). GR requires FAD and NADPH to facilitate this reaction; first a hydride must be transferred from NADPH to FAD. The reduced flavin can then act as a nucleophile to attack the disulfide, this forms the C4a-cysteine adduct. Elimination of this adduct results in a flavin-thiolate charge-transfer complex. Cytochrome P450 type enzymes that catalyze monooxygenase (hydroxylation) reactions are dependent on

7470-458: The ribose sugar via a glycosidic bond are thymine , cytosine and uracil (which is only found in RNA). Uridine monophosphate biosynthesis involves an enzyme that is located in the mitochondrial inner membrane and multifunctional enzymes that are located in the cytosol . After the uridine nucleotide base is synthesized, the other bases, cytosine and thymine are synthesized. Cytosine biosynthesis

7560-413: The simultaneous reduction of enzyme-bound flavin. GOX exists as a homodimer, with each subunit binding one FAD molecule. Crystal structures show that FAD binds in a deep pocket of the enzyme near the dimer interface. Studies showed that upon replacement of FAD with 8-hydroxy-5-carba-5-deaza FAD, the stereochemistry of the reaction was determined by reacting with the re face of the flavin. During turnover,

7650-442: The small intestine and then transported to cells via carrier proteins. Riboflavin kinase (EC 2.7.1.26) adds a phosphate group to riboflavin to produce flavin mononucleotide, and then FAD synthetase attaches an adenine nucleotide ; both steps require ATP . Bacteria generally have one bi-functional enzyme, but archaea and eukaryotes usually employ two distinct enzymes. Current research indicates that distinct isoforms exist in

7740-419: The standard amino acids includes a primary amino group , a carboxyl group and the functional group attached to the α-carbon . The different amino acids are identified by the functional group. As a result of the three different groups attached to the α-carbon, amino acids are asymmetrical molecules . For all standard amino acids, except glycine , the α-carbon is a chiral center . In the case of glycine,

7830-402: The transfer of two electrons from FAD to the P450. Two types of P450 systems are found in eukaryotes. The P450 systems that are located in the endoplasmic reticulum are dependent on a cytochrome P-450 reductase (CPR) that contains both an FAD and an FMN . The two electrons on reduced FAD (FADH 2 ) are transferred one at a time to FMN and then a single electron is passed from FMN to the heme of

7920-408: The two synthetic pathways is the diaminopimelic acid pathway; it consists of several enzymatic reactions that add carbon groups to aspartate to yield lysine: The serine family of amino acid includes: serine, cysteine , and glycine . Most microorganisms and plants obtain the sulfur for synthesizing methionine from the amino acid cysteine. Furthermore, the conversion of serine to glycine provides

8010-445: The use of a flavin-N(5)-oxide rather than a flavin-C(4a)-(hydro)peroxide. Chorismate synthase (CS) catalyzes the last step in the shikimate pathway —the formation of chorismate. Two classes of CS are known, both of which require FMN , but are divided on their need for NADPH as a reducing agent. The proposed mechanism for CS involves radical species. The radical flavin species has not been detected spectroscopically without using

8100-524: The α-carbon has two hydrogen atoms, thus adding symmetry to this molecule. With the exception of proline , all of the amino acids found in life have the L-isoform conformation. Proline has a functional group on the α-carbon that forms a ring with the amino group. One major step in amino acid biosynthesis involves incorporating a nitrogen group onto the α-carbon. In cells, there are two major pathways of incorporating nitrogen groups. One pathway involves

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