In biochemistry , isozymes (also known as isoenzymes or more generally as multiple forms of enzymes ) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. Isozymes usually have different kinetic parameters (e.g. different K M values), or are regulated differently. They permit the fine-tuning of metabolism to meet the particular needs of a given tissue or developmental stage.
21-401: 4V06 121278 216343 ENSG00000139287 ENSMUSG00000006764 Q8IWU9 Q8CGV2 NM_173353 NM_173391 NP_775489 NP_775567 Tryptophan hydroxylase 2 ( TPH2 ) is an isozyme of tryptophan hydroxylase found in vertebrates. In humans, TPH2 is primarily expressed in the serotonergic neurons of the brain, with the highest expression in the raphe nucleus of
42-436: A DNA sequence, often on a particular chromosome . In the 1960s, researchers Joseph Gall and Mary Lou Pardue found that molecular hybridization could be used to identify the position of DNA sequences in situ (i.e., in their natural positions within a chromosome). In 1969, the two scientists published a paper demonstrating that radioactive copies of a ribosomal DNA sequence could be used to detect complementary DNA sequences in
63-478: A single PCPA injection resulted in the lowest level of serotonin production occurring on day 2 and returning to control values on day 7. Drugs such as MDMA and methamphetamine have been shown to lower levels of this enzyme which may result in periods of low serotonin levels following drug use. In a study investigating the effects of Fenclonine on humans, the greatly lowered serotonin levels were associated with "fatigue, dizziness, nausea, uneasiness [anxiety], fullness in
84-527: Is a phenomenon in which single-stranded deoxyribonucleic acid ( DNA ) or ribonucleic acid ( RNA ) molecules anneal to complementary DNA or RNA . Though a double-stranded DNA sequence is generally stable under physiological conditions, changing these conditions in the laboratory (generally by raising the surrounding temperature) will cause the molecules to separate into single strands. These strands are complementary to each other but may also be complementary to other sequences present in their surroundings. Lowering
105-421: Is taken advantage of in numerous molecular biology techniques. Overall, genetic relatedness of two species can be determined by hybridizing segments of their DNA ( DNA-DNA hybridization ). Due to sequence similarity between closely related organisms, higher temperatures are required to melt such DNA hybrids when compared to more distantly related organisms. A variety of different methods use hybridization to pinpoint
126-594: The beta cells of the pancreas , or initiation of glycogen synthesis by liver cells. Both these processes must only occur when glucose is abundant. 1.) The enzyme lactate dehydrogenase is a tetramer made of two different sub-units, the H-form and the M-form. These combine in different combinations depending on the tissue: Heat (at 60 °C) serum in humans 2.) Isoenzymes of creatine phosphokinase: Creatine kinase (CK) or creatine phosphokinase (CPK) catalyses
147-501: The electric charge of the enzyme are simple to identify by gel electrophoresis , and this forms the basis for the use of isozymes as molecular markers . To identify isozymes, a crude protein extract is made by grinding animal or plant tissue with an extraction buffer, and the components of extract are separated according to their charge by gel electrophoresis. Historically, this has usually been done using gels made from potato starch , but acrylamide gels provide better resolution. All
168-448: The coding sequence of the gene. As with any other new mutations, there are three things that may happen to a new allozyme: An example of an isozyme is glucokinase , a variant of hexokinase which is not inhibited by glucose 6-phosphate . Its different regulatory features and lower affinity for glucose (compared to other hexokinases), allow it to serve different functions in cells of specific organs, such as control of insulin release by
189-418: The enzymes are still functional after separation ( native gel electrophoresis ), and provides the greatest challenge to using isozymes as a laboratory technique. Isoenzymes differ in kinetics (they have different K M and V max values). Population genetics is essentially a study of the causes and effects of genetic variation within and between populations, and in the past, isozymes have been amongst
210-467: The head [a feeling of pressure in the head] paresthesias [a pricking, pins-and-needles, burning, and/or aching sensation--typically the limbs], headache, and constipation". This article on a gene on human chromosome 12 is a stub . You can help Misplaced Pages by expanding it . Isozyme In many cases, isozymes are encoded by homologous genes that have diverged over time. Strictly speaking, enzymes with different amino acid sequences that catalyse
231-614: The interconversion of phospho creatine to creatine . CPK exists in 3 isoenzymes. Each isoenzymes is a dimer of 2 subunits M (muscle), B (brain) or both 3.) Isoenzymes of alkaline phosphatase: Six isoenzymes have been identified. The enzyme is a monomer, the isoenzymes are due to the differences in the carbohydrate content (sialic acid residues). The most important ALP isoenzymes are α 1 -ALP, α 2 -heat labile ALP, α 2 -heat stable ALP, pre-β ALP and γ-ALP. Increase in α 2 -heat labile ALP suggests hepatitis whereas pre-β ALP indicates bone diseases. Isozymes (and allozymes) are variants of
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#1732791548551252-512: The maintenance of vascular tone and gut motility.[supplied by OMIM] Disabling this enzyme with drugs (especially p-chlorophenylalanine aka PCPA and Fenclonine) has allowed researchers to investigate the effects of very low serotonin levels on humans and others animals, and by extension, gain insights into the functions of serotonin systems more broadly (such as hypersexuality in rodents as well as increased aggression and hypersexuality cats following PCPA administration). In rat brain, administration of
273-494: The midbrain. Until the discovery of TPH2 in 2003, serotonin levels in the central nervous system were believed to be regulated by serotonin synthesis in peripheral tissues, in which tryptophan hydroxylase is the dominant form. Tryptophan hydroxylase (TPH; EC 1.14.16.4) is the rate-limiting enzyme in the synthesis of serotonin (5-hydroxytryptamine, or 5HT). 5HT is causally involved in numerous central nervous activities, and it has several functions in peripheral tissues, including
294-564: The most widely used molecular markers for this purpose. Although they have now been largely superseded by more informative DNA -based approaches (such as direct DNA sequencing , single nucleotide polymorphisms and microsatellites ), they are still among the quickest and cheapest marker systems to develop, and remain (as of 2005 ) an excellent choice for projects that only need to identify low levels of genetic variation, e.g. quantifying mating systems . Nucleic acid hybridization In molecular biology, hybridization (or hybridisation )
315-434: The origin of a DNA sample, including the polymerase chain reaction (PCR). In another technique, short DNA sequences are hybridized to cellular mRNAs to identify expressed genes. Pharmaceutical drug companies are exploring the use of antisense RNA to bind to undesired mRNA, preventing the ribosome from translating the mRNA into protein. Fluorescence in situ hybridization (FISH) is a laboratory method used to detect and locate
336-588: The original, then it is likely that one or the other will be lost as mutations accumulate, resulting in a pseudogene . However, if the mutations do not immediately prevent the enzyme from functioning, but instead modify either its function, or its pattern of expression , then the two variants may both be favoured by natural selection and become specialised to different functions. For example, they may be expressed at different stages of development or in different tissues. Allozymes may result from point mutations or from insertion-deletion ( indel ) events that affect
357-413: The product of different genes and thus represent different loci (described as isozymes ) and (2) enzymes that are the product of different alleles of the same gene (described as allozymes ). Isozymes are usually the result of gene duplication , but can also arise from polyploidisation or nucleic acid hybridization . Over evolutionary time, if the function of the new variant remains identical to
378-452: The proteins from the tissue are present in the gel, so that individual enzymes must be identified using an assay that links their function to a staining reaction. For example, detection can be based on the localised precipitation of soluble indicator dyes such as tetrazolium salts which become insoluble when they are reduced by cofactors such as NAD or NADP , which generated in zones of enzyme activity. This assay method requires that
399-585: The same enzyme. Unless they are identical in their biochemical properties, for example their substrates and enzyme kinetics , they may be distinguished by a biochemical assay . However, such differences are usually subtle, particularly between allozymes which are often neutral variants . This subtlety is to be expected, because two enzymes that differ significantly in their function are unlikely to have been identified as isozymes . While isozymes may be almost identical in function, they may differ in other ways. In particular, amino acid substitutions that change
420-437: The same reaction are isozymes if encoded by different genes, or allozymes if encoded by different alleles of the same gene ; the two terms are often used interchangeably. Isozymes were first described by R. L. Hunter and Clement Markert (1957) who defined them as different variants of the same enzyme having identical functions and present in the same individual . This definition encompasses (1) enzyme variants that are
441-430: The surrounding temperature allows the single-stranded molecules to anneal or “hybridize” to each other. DNA replication and transcription of DNA into RNA both rely upon nucleotide hybridization, as do molecular biology techniques including Southern blots and Northern blots , the polymerase chain reaction (PCR), and most approaches to DNA sequencing . Hybridization is a basic property of nucleotide sequences and
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