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65-460: The river was heavily polluted with untreated sewage, agricultural fertilizer, and toxic chemicals from local mining sites, including cyanide , arsenic , lead , and cadmium . One notable incident occurred on January 30, 2000, when a tailings impoundment at the Baia Mare mine burst, releasing 50 to 100 tons of cyanide and heavy metals into the river. The Săsar, locally known as the "dead river,"

130-398: A −C≡N functional group are called nitriles . An example of a nitrile is acetonitrile , CH 3 −C≡N . Nitriles usually do not release cyanide ions. A functional group with a hydroxyl −OH and cyanide −CN bonded to the same carbon atom is called cyanohydrin ( R 2 C(OH)CN ). Unlike nitriles, cyanohydrins do release poisonous hydrogen cyanide . Cyanide is basic. The p K

195-417: A UV light gives a green/blue glow if the test is positive. Hydrogenase A hydrogenase is an enzyme that catalyses the reversible oxidation of molecular hydrogen (H 2 ), as shown below: Hydrogen uptake ( 1 ) is coupled to the reduction of electron acceptors such as oxygen , nitrate , sulfate , carbon dioxide (CO 2 ), and fumarate . On the other hand, proton reduction ( 2 )

260-408: A of hydrogen cyanide is 9.21. Thus, addition of acids stronger than hydrogen cyanide to solutions of cyanide salts releases hydrogen cyanide . Cyanide is unstable in water, but the reaction is slow until about 170 °C. It undergoes hydrolysis to give ammonia and formate , which are far less toxic than cyanide: Cyanide hydrolase is an enzyme that catalyzes this reaction. Because of

325-483: A tailing pond or spent heap, the recoverable gold having been removed. The metal is recovered from the "pregnant solution" by reduction with zinc dust or by adsorption onto activated carbon . This process can result in environmental and health problems. A number of environmental disasters have followed the overflow of tailing ponds at gold mines. Cyanide contamination of waterways has resulted in numerous cases of human and aquatic species mortality. Aqueous cyanide

390-465: A cysteine derived thiol. The diiron co-factor includes two iron atoms, connected by a bridging aza-dithiolate ligand (-SCH 2 -NH-CH 2 S-, adt), the iron atoms are coordinated by carbonyl and cyanide ligands. [FeFe]-hydrogenases can be separated into four distinct phylogenetic groups A−D. Group A consists of prototypical and bifurcating [FeFe]-hydrogenases. In nature, prototypical [FeFe]-hydrogenases perform hydrogen turnover using ferredoxin as

455-423: A long distance; the active site structures remain unchanged during the whole process. In [Fe]-only hydrogenases, however, electrons are directly delivered to the active site via a short distance. Methenyl-H4MPT , a cofactor, directly accepts the hydride from H 2 in the process. [Fe]-only hydrogenase is also known as H 2 -forming methylenetetrahydromethanopterin (methylene-H4MPT) dehydrogenase, because its function

520-445: A metabolite arises from the expression of metalloenzymes known as hydrogenases. Hydrogenases are sub-classified into three different types based on the active site metal content: iron-iron hydrogenase, nickel-iron hydrogenase, and iron hydrogenase. Hydrogenases catalyze, sometimes reversibly, H 2 uptake. The [FeFe] and [NiFe] hydrogenases are true redox catalysts, driving H 2 oxidation and proton (H ) reduction (equation 3 ),

585-486: A reactive species at the active site of [FeFe] hydrogenases, and then damages its [4Fe-4S] domain. Cohen et al. investigated how oxygen can reach the active site that is buried inside the protein body by molecular dynamics simulation approach; their results indicate that O 2 diffuses through mainly two pathways that are formed by enlargement of and interconnection between cavities during dynamic motion. These works, in combination with other reports, suggest that inactivation

650-722: A redox partner while bifurcating types perform the same reaction using both ferredoxin and NAD(H) as electron donor or acceptor. In order to conserve energy, anaerobic bacteria use electron bifurcation where exergonic and endergonic redox reactions are coupled to circumvent thermodynamic barriers . Group A comprises the best characterized and catalytically most active enzymes such as the [FeFe]-hydrogenase from Chlamydomonas reinhardtii ( Cr HydA1), Desulfovibrio desulfuricans ( Dd HydAB or Dd H), and Clostridium pasteurianum and Clostridium acetobutylicum ( Cp HydA1 and Ca HydA1, referred to as Cp I and Ca I). No representative examples of Group B has been characterized yet but it

715-511: A relatively low overpotential . In fact, its catalytic activity is more effective than platinum, which is the best known catalyst for H 2 evolution reaction. Among three different types of hydrogenases, [FeFe] hydrogenases is considered as a strong candidate for an integral part of the solar H 2 production system since they offer an additional advantage of high TOF (over 9000 s ) . Low overpotential and high catalytic activity of [FeFe] hydrogenases are accompanied by high O 2 sensitivity. It

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780-460: A river in Maramureș County is a stub . You can help Misplaced Pages by expanding it . Cyanide In chemistry , cyanide (from Greek kyanos  ' dark blue ') is a chemical compound that contains a C≡N functional group . This group, known as the cyano group , consists of a carbon atom triple-bonded to a nitrogen atom. In inorganic cyanides, the cyanide group

845-552: A similar location on the bacterial gene and share similar domain structure to a subclass from Group E but it lacks the PAS domain. Within Group D, the [FeFe]-hydrogenase from Thermoanaerobacter mathranii (referred to as Tam HydS) has been characterized. 5,10-methenyltetrahydromethanopterin hydrogenase (EC 1.12.98.2 ) found in methanogenic Archaea contains neither nickel nor iron-sulfur clusters but an iron-containing cofactor that

910-623: A very high affinity for hydrogen. Hydrogen is able to penetrate narrow channels in the enzyme that oxygen molecules cannot enter. This allows bacteria such as Mycobacterium smegmatis to utilize the small amount of hydrogen in the atmosphere as a source of energy when other sources are lacking. The hydrogenases containing a di-iron center with a bridging dithiolate cofactor are called [FeFe] hydrogenases. Three families of [FeFe] hydrogenases are recognized: In contrast to [NiFe] hydrogenases, [FeFe] hydrogenases are generally more active in production of molecular hydrogen. Turnover frequency (TOF) in

975-532: Is a reductant and is oxidized by strong oxidizing agents such as molecular chlorine ( Cl 2 ), hypochlorite ( ClO ), and hydrogen peroxide ( H 2 O 2 ). These oxidizers are used to destroy cyanides in effluents from gold mining . The cyanide anion reacts with transition metals to form M-CN bonds . This reaction is the basis of cyanide's toxicity. The high affinities of metals for this anion can be attributed to its negative charge, compactness, and ability to engage in π-bonding. Among

1040-421: Is a gas, making it more indiscriminately dangerous, however it is lighter than air and rapidly disperses up into the atmosphere, which makes it ineffective as a chemical weapon . Because of the high stability of their complexation with iron , ferrocyanides ( Sodium ferrocyanide E535, Potassium ferrocyanide E536, and Calcium ferrocyanide E538 ) do not decompose to lethal levels in the human body and are used in

1105-401: Is believed to be the place where catalysis takes place, is also a metallocluster, and each iron is coordinated by carbon monoxide (CO) and cyanide (CN ) ligands. The [NiFe] hydrogenases are heterodimeric proteins consisting of small (S) and large (L) subunits. The small subunit contains three iron-sulfur clusters while the large subunit contains the active site, a nickel-iron centre which

1170-436: Is concentrated on carbon C. Cyanides are produced by certain bacteria , fungi , and algae . It is an antifeedant in a number of plants. Cyanides are found in substantial amounts in certain seeds and fruit stones, e.g., those of bitter almonds , apricots , apples , and peaches . Chemical compounds that can release cyanide are known as cyanogenic compounds. In plants, cyanides are usually bound to sugar molecules in

1235-1486: Is connected to the solvent by a molecular tunnel. In some [NiFe] hydrogenases, one of the Ni-bound cysteine residues is replaced by selenocysteine . On the basis of sequence similarity, however, the [NiFe] and [NiFeSe] hydrogenases should be considered a single superfamily. To date, periplasmic, cytoplasmic, and cytoplasmic membrane-bound hydrogenases have been found. The [NiFe] hydrogenases, when isolated, are found to catalyse both H 2 evolution and uptake, with low-potential multihaem cytochromes such as cytochrome c 3 acting as either electron donors or acceptors, depending on their oxidation state. Generally speaking, however, [NiFe] hydrogenases are more active in oxidizing H 2 . A wide spectrum of H 2 affinities have also been observed in H 2 -oxidizing hydrogenases. Like [FeFe] hydrogenases, [NiFe] hydrogenases are known to be usually deactivated by molecular oxygen (O 2 ). Hydrogenase from Ralstonia eutropha , and several other so-called Knallgas-bacteria, were found to be oxygen-tolerant. The soluble [NiFe] hydrogenase from Ralstonia eutropha H16 can be conveniently produced on heterotrophic growth media. This finding increased hope that hydrogenases can be used in photosynthetic production of molecular hydrogen via splitting water. Another [NiFe], called Huc or Hyd1 or cyanobacterial-type uptake hydrogenase, has been found to be oxygen insensitive while having

1300-493: Is coupled to the oxidation of electron donors such as ferredoxin (FNR), and serves to dispose excess electrons in cells (essential in pyruvate fermentation). Both low-molecular weight compounds and proteins such as FNRs, cytochrome c 3 , and cytochrome c 6 can act as physiological electron donors or acceptors for hydrogenases. It has been estimated that 99% of all organisms utilize hydrogen , H 2 . Most of these species are microbes and their ability to use H 2 as

1365-456: Is governed by two phenomena: diffusion of O 2 to the active site, and destructive modification of the active site. Despite these findings, research is still under progress for engineering oxygen tolerance in hydrogenases. While researchers have found oxygen-tolerant [NiFe] hydrogenases, they are only efficient in hydrogen uptake and not production . Bingham et al.'s recent success in engineering [FeFe] hydrogenase from Clostridium pasteurianum

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1430-428: Is hydrolyzed rapidly, especially in sunlight. It can mobilize some heavy metals such as mercury if present. Gold can also be associated with arsenopyrite (FeAsS), which is similar to iron pyrite (fool's gold), wherein half of the sulfur atoms are replaced by arsenic . Gold-containing arsenopyrite ores are similarly reactive toward inorganic cyanide. The second major application of alkali metal cyanides (after mining)

1495-418: Is in the production of CN-containing compounds, usually nitriles. Acyl cyanides are produced from acyl chlorides and cyanide. Cyanogen , cyanogen chloride , and the trimer cyanuric chloride are derived from alkali metal cyanides. The cyanide compound sodium nitroprusside is used mainly in clinical chemistry to measure urine ketone bodies mainly as a follow-up to diabetic patients. On occasion, it

1560-422: Is mainly produced for the mining of silver and gold : It helps dissolve these metals allowing separation from the other solids. In the cyanide process , finely ground high-grade ore is mixed with the cyanide (at a ratio of about 1:500 parts NaCN to ore); low-grade ores are stacked into heaps and sprayed with a cyanide solution (at a ratio of about 1:1000 parts NaCN to ore). The precious metals are complexed by

1625-408: Is necessary to engineer them O 2 -tolerant for use in solar H 2 production since O 2 is a by-product of water splitting reaction. Past research efforts by various groups around the world have focused on understanding the mechanisms involved in O 2 -inactivation of hydrogenases. For instance, Stripp et al. relied on protein film electrochemistry and discovered that O 2 first converts into

1690-538: Is phylogenetically distinct even when it shares similar amino acid motifs around the H-cluster as Group A [FeFe]-hydrogenases. Group C has been classified as "sensory" based on the presence of a Per-Arnt-Sim domain . One example of a Group C [FeFe]-hydrogenase is from Thermotoga maritima ( Tm HydS) which shows only modest catalytic rates compared to Group A enzymes and an apparent high sensitivity toward hydrogen (H 2 ). A closely related subclass from Group D has

1755-427: Is present as the cyanide anion C≡N . This anion is extremely poisonous . Soluble salts such as sodium cyanide (NaCN) and potassium cyanide (KCN) are highly toxic. Hydrocyanic acid , also known as hydrogen cyanide, or HCN, is a highly volatile liquid that is produced on a large scale industrially. It is obtained by acidification of cyanide salts. Organic cyanides are usually called nitriles . In nitriles,

1820-404: Is the reversible reduction of methenyl-H4MPT to methylene-H4MPT. The hydrogenation of a methenyl-H4MPT+ occurs instead of H 2 oxidation/production, which is the case for the other two types of hydrogenases. While the exact mechanism of the catalysis is still under study, recent finding suggests that molecular hydrogen is first heterolytically cleaved by Fe(II), followed by transfer of hydride to

1885-688: Is unsuitable for bathing, washing, or fishing. The World Health Organization has identified the Baia Mare region as a "health risk hotspot." The Săsar flows into the Lăpuș, which in turn flows into the Someș , a tributary of the Danube via the Tisza . Pollution in the Săsar thus eventually reaches Romania, Hungary, Serbia, and Bulgaria. The following rivers are tributaries to the river Săsar: This article related to

1950-415: Is used in emergency medical situations to produce a rapid decrease in blood pressure in humans; it is also used as a vasodilator in vascular research. The cobalt in artificial vitamin B 12 contains a cyanide ligand as an artifact of the purification process; this must be removed by the body before the vitamin molecule can be activated for biochemical use. During World War I , a copper cyanide compound

2015-443: Is used to achieve a blue color on cast bronze sculptures during the final finishing stage of the sculpture. On its own, it will produce a very dark shade of blue and is often mixed with other chemicals to achieve the desired tint and hue. It is applied using a torch and paint brush while wearing the standard safety equipment used for any patina application: rubber gloves, safety glasses, and a respirator. The actual amount of cyanide in

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2080-460: Is used to measure the temperature of interstellar gas clouds . Hydrogen cyanide is produced by the combustion or pyrolysis of certain materials under oxygen-deficient conditions. For example, it can be detected in the exhaust of internal combustion engines and tobacco smoke. Certain plastics , especially those derived from acrylonitrile , release hydrogen cyanide when heated or burnt. In IUPAC nomenclature , organic compounds that have

2145-442: The −C≡N group is linked by a single covalent bond to carbon. For example, in acetonitrile ( CH 3 −C≡N ), the cyanide group is bonded to methyl ( −CH 3 ). Although nitriles generally do not release cyanide ions, the cyanohydrins do and are thus toxic. The cyanide ion C≡N is isoelectronic with carbon monoxide C≡O and with molecular nitrogen N≡N. A triple bond exists between C and N. The negative charge

2210-517: The heart , are particularly affected. This is an example of histotoxic hypoxia . The most hazardous compound is hydrogen cyanide , which is a gas and kills by inhalation. For this reason, an air respirator supplied by an external oxygen source must be worn when working with hydrogen cyanide. Hydrogen cyanide is produced by adding acid to a solution containing a cyanide salt. Alkaline solutions of cyanide are safer to use because they do not evolve hydrogen cyanide gas. Hydrogen cyanide may be produced in

2275-412: The mitochondria of eukaryotic cells. It attaches to the iron within this protein. The binding of cyanide to this enzyme prevents transport of electrons from cytochrome c to oxygen. As a result, the electron transport chain is disrupted, meaning that the cell can no longer aerobically produce ATP for energy. Tissues that depend highly on aerobic respiration , such as the central nervous system and

2340-505: The 1930s, and they have since attracted interest from many researchers including inorganic chemists who have synthesized a variety of hydrogenase mimics . The soluble [NiFe] hydrogenase from Ralstonia eutropha H16 is a promising candidate enzyme for H 2 -based biofuel application as it favours H 2 oxidation and is relatively oxygen-tolerant. It can be produced on heterotrophic growth media and purified via anion exchange and size exclusion chromatography matrices. Understanding

2405-530: The United States to kill coyotes and other canids. Cyanide is also used for pest control in New Zealand , particularly for possums , an introduced marsupial that threatens the conservation of native species and spreads tuberculosis amongst cattle. Possums can become bait shy but the use of pellets containing the cyanide reduces bait shyness. Cyanide has been known to kill native birds, including

2470-472: The [Fe] hydrogenases catalyze the reversible heterolytic cleavage of H 2 shown by reaction ( 4 ). Although originally believed to be "metal-free", the [Fe]-only hydrogenases contain Fe at the active site and no iron-sulfur clusters. [NiFe] and [FeFe] hydrogenases have some common features in their structures: Each enzyme has an active site and a few Fe-S clusters that are buried in protein. The active site, which

2535-407: The antidote was to generate a large pool of ferric iron ( Fe ) to compete for cyanide with cytochrome a 3 (so that cyanide will bind to the antidote rather than the enzyme). The nitrites oxidize hemoglobin to methemoglobin , which competes with cytochrome oxidase for the cyanide ion. Cyanmethemoglobin is formed and the cytochrome oxidase enzyme is restored. The major mechanism to remove

2600-501: The bamboo, has developed a high tolerance to cyanide. The hydrogenase enzymes contain cyanide ligands attached to iron in their active sites. The biosynthesis of cyanide in the NiFe hydrogenases proceeds from carbamoyl phosphate , which converts to cysteinyl thiocyanate , the CN donor. The cyanide radical CN has been identified in interstellar space . Cyanogen , (CN) 2 ,

2665-458: The blue color to blueprints , bluing , and cyanotypes . The principal process used to manufacture cyanides is the Andrussow process in which gaseous hydrogen cyanide is produced from methane and ammonia in the presence of oxygen and a platinum catalyst . Sodium cyanide, the precursor to most cyanides, is produced by treating hydrogen cyanide with sodium hydroxide : Among

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2730-407: The capture and storage of renewable energy as fuel with use on demand. This can be demonstrated through the chemical storage of electricity obtained from a renewable source (e.g. solar, wind, hydrothermal ) as H 2 during periods of low energy demands. When energy is desired, H 2 can be oxidized to produce electricity. This is one solution to the challenge in the development of technologies for

2795-449: The carbocation of the acceptor. The molecular mechanism by which protons are converted into hydrogen molecules within hydrogenases is still under extensive study. One popular approach employs mutagenesis to elucidate roles of amino acids and/or ligands in different steps of catalysis such as intramolecular transport of substrates. For instance, Cornish et al. conducted mutagenesis studies and found out that four amino acids located along

2860-472: The catalytic mechanism of hydrogenase might help scientists design clean biological energy sources, such as algae, that produce hydrogen. Various systems are capable of splitting water into O 2 and H from incident sunlight. Likewise, numerous catalysts, either chemical or biological, can reduce the produced H into H 2 . Different catalysts require unequal overpotential for this reduction reaction to take place. Hydrogenases are attractive since they require

2925-512: The combustion of polyurethanes ; for this reason, polyurethanes are not recommended for use in domestic and aircraft furniture. Oral ingestion of a small quantity of solid cyanide or a cyanide solution of as little as 200 mg, or exposure to airborne cyanide of 270 ppm , is sufficient to cause death within minutes. Organic nitriles do not readily release cyanide ions, and so have low toxicities. By contrast, compounds such as trimethylsilyl cyanide (CH 3 ) 3 SiCN readily release HCN or

2990-420: The cyanide anions to form soluble derivatives, e.g., [Ag(CN) 2 ] (dicyanoargentate(I)) and [Au(CN) 2 ] (dicyanoaurate(I)). Silver is less "noble" than gold and often occurs as the sulfide, in which case redox is not invoked (no O 2 is required). Instead, a displacement reaction occurs: The "pregnant liquor" containing these ions is separated from the solids, which are discarded to

3055-410: The cyanide anion's high nucleophilicity , cyano groups are readily introduced into organic molecules by displacement of a halide group (e.g., the chloride on methyl chloride ). In general, organic cyanides are called nitriles. In organic synthesis, cyanide is a C-1 synthon ; i.e., it can be used to lengthen a carbon chain by one, while retaining the ability to be functionalized . The cyanide ion

3120-602: The cyanide from the body is by enzymatic conversion to thiocyanate by the mitochondrial enzyme rhodanese . Thiocyanate is a relatively non-toxic molecule and is excreted by the kidneys. To accelerate this detoxification, sodium thiosulfate is administered to provide a sulfur donor for rhodanese , needed in order to produce thiocyanate. Minimum risk levels (MRLs) may not protect for delayed health effects or health effects acquired following repeated sublethal exposure, such as hypersensitivity, asthma , or bronchitis . MRLs may be revised after sufficient data accumulates. Cyanide

3185-525: The cyanide ion upon contact with water. Hydroxocobalamin reacts with cyanide to form cyanocobalamin , which can be safely eliminated by the kidneys. This method has the advantage of avoiding the formation of methemoglobin (see below). This antidote kit is sold under the brand name Cyanokit and was approved by the U.S. FDA in 2006. An older cyanide antidote kit included administration of three substances: amyl nitrite pearls (administered by inhalation), sodium nitrite , and sodium thiosulfate . The goal of

3250-496: The endangered kiwi . Cyanide is also effective for controlling the dama wallaby , another introduced marsupial pest in New Zealand. A licence is required to store, handle and use cyanide in New Zealand. Cyanides are used as insecticides for fumigating ships. Cyanide salts are used for killing ants, and have in some places been used as rat poison (the less toxic poison arsenic is more common). Potassium ferrocyanide

3315-420: The food industry as, e.g., an anticaking agent in table salt . Cyanide is quantified by potentiometric titration , a method widely used in gold mining. It can also be determined by titration with silver ion. Some analyses begin with an air-purge of an acidified boiling solution, sweeping the vapors into a basic absorber solution. The cyanide salt absorbed in the basic solution is then analyzed. Because of

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3380-417: The form of cyanogenic glycosides and defend the plant against herbivores . Cassava roots (also called manioc), an important potato -like food grown in tropical countries (and the base from which tapioca is made), also contain cyanogenic glycosides. The Madagascar bamboo Cathariostachys madagascariensis produces cyanide as a deterrent to grazing. In response, the golden bamboo lemur , which eats

3445-463: The generation of a transmembrane protonmotive force. There is a possibility that hydrogenases have been responsible for bioremediation of chlorinated compounds. Hydrogenases proficient in H 2 uptake can help heavy metal contaminants to be recovered in intoxicated forms. These uptake hydrogenases have been recently discovered in pathogenic bacteria and parasites and are believed to be involved in their virulence. Hydrogenases were first discovered in

3510-488: The mixture varies according to the recipes used by each foundry. Cyanide is also used in jewelry -making and certain kinds of photography such as sepia toning . Although usually thought to be toxic, cyanide and cyanohydrins increase germination in various plant species. Deliberate cyanide poisoning of humans has occurred many times throughout history. Common salts such as sodium cyanide are involatile but water-soluble, so are poisonous by ingestion. Hydrogen cyanide

3575-457: The model that describes how hydrogen molecules are oxidized or produced within the active site of [FeFe] hydrogenases. While more research and experimental data are required to complete our understanding of the mechanism, these findings have allowed scientists to apply the knowledge in, e.g., building artificial catalysts mimicking active sites of hydrogenases. Assuming that the Earth's atmosphere

3640-435: The most important cyanide coordination compounds are the potassium ferrocyanide and the pigment Prussian blue , which are both essentially nontoxic due to the tight binding of the cyanides to a central iron atom. Prussian blue was first accidentally made around 1706, by heating substances containing iron and carbon and nitrogen, and other cyanides made subsequently (and named after it). Among its many uses, Prussian blue gives

3705-415: The most toxic cyanides are hydrogen cyanide (HCN), sodium cyanide (NaCN), potassium cyanide (KCN), and calcium cyanide (Ca(CN)₂). These compounds are extremely poisonous and require careful handling to avoid severe health risks. The cyanide anion is an inhibitor of the enzyme cytochrome c oxidase (also known as aa 3 ), the fourth complex of the electron transport chain found in the inner membrane of

3770-460: The notorious toxicity of cyanide, many methods have been investigated. Benzidine gives a blue coloration in the presence of ferricyanide . Iron(II) sulfate added to a solution of cyanide, such as the filtrate from the sodium fusion test , gives prussian blue . A solution of para -benzoquinone in DMSO reacts with inorganic cyanide to form a cyano phenol , which is fluorescent . Illumination with

3835-401: The order of 10,000 s have been reported in literature for [FeFe] hydrogenases from Clostridium pasteurianum . This has led to intense research focusing on use of [FeFe] hydrogenase for sustainable production of H 2 . The active site of the diiron hydrogenase is known as the H-cluster. The H-cluster consists of a [4Fe4S] cubane-shaped structure, coupled to the low valent diiron co-factor by

3900-518: The primary role of hydrogenases are believed to be energy generation, and this can be sufficient to sustain an ecosystem. Recent studies have revealed other biological functions of hydrogenases. To begin with, bidirectional hydrogenases can also act as "valves" to control excess reducing equivalents, especially in photosynthetic microorganisms. Such a role makes hydrogenases play a vital role in anaerobic metabolism . Moreover, hydrogenases may also be involved in membrane-linked energy conservation through

3965-518: The putative channel connecting the active site and protein surface are critical to enzymatic function of [FeFe] hydrogenase from Clostridium pasteurianum (CpI). On the other hand, one can also rely on computational analysis and simulations. Nilsson Lill and Siegbahn have recently taken this approach in investigating the mechanism by which [NiFe] hydrogenases catalyze H 2 cleavage. The two approaches are complementary and can benefit one another. In fact, Cao and Hall combined both approaches in developing

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4030-426: Was also limited to retained activity (during exposure to oxygen) for H 2 consumption, only. Typical enzymatic biofuel cells involve the usage of enzymes as electrocatalysts at either both cathode and anode or at one electrode. In hydrogenase-based biofuel cells, hydrogenase enzymes are present at the anode for H 2 oxidation. The bidirectional or reversible reaction catalyzed by hydrogenase allows for

4095-509: Was briefly used by Japanese physicians for the treatment of tuberculosis and leprosy . Cyanides are illegally used to capture live fish near coral reefs for the aquarium and seafood markets. The practice is controversial, dangerous, and damaging but is driven by the lucrative exotic fish market. Poachers in Africa have been known to use cyanide to poison waterholes, to kill elephants for their ivory. M44 cyanide devices are used in

4160-464: Was initially rich in hydrogen, scientists hypothesize that hydrogenases were evolved to generate energy from/as molecular H 2 . Accordingly, hydrogenases can either help microorganisms to proliferate under such conditions, or to set up ecosystems empowered by H 2 . Microbial communities driven by molecular hydrogen have, in fact, been found in deep-sea settings where other sources of energy from photosynthesis are not available. Based on these grounds,

4225-416: Was recently characterized by X-ray diffraction. Unlike the other two types, [Fe]-only hydrogenases are found only in some hydrogenotrophic methanogenic archaea. They also feature a fundamentally different enzymatic mechanism in terms of redox partners and how electrons are delivered to the active site. In [NiFe] and [FeFe] hydrogenases, electrons travel through a series of metallorganic clusters that comprise

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