Alcohol dehydrogenase 89198 225943863 2008-07-16T03:32:00Z 71.196.135.208 [[Image:AlcoholDehydrogenase-1A4U.png|thumb|Alcohol Dehydrogenase]] [[Image:ladh.jpg|Image:ladh.jpg]|frame|right|LADH(Liver Alcohol Dehyrogenase)]] '''Alcohol dehydrogenase (ADH)''' is an enzyme discovered in the mid-1960s in [[Drosophila melanogaster]]. Since then, there has been extensive research on the enzyme.<ref>Sofer, W. and Martin, F. Presley. Annual Reviews. Analysis of Alcohol Dehydrogenase Gene Expression in Drosophila. 21 (1987):203-25.</ref> Alcohol dehydrogenase is a [[dimer]], weighing 80 kDa.<ref>Hammes-Schiffer, Sharon and Benkoviv, Stephen J. Relating Protein Motion to Catalysis. Annual Review of Biochemistry. 75(2006):519-41.</ref> '''Alcohol dehydrogenases''' ({{EC number|1.1.1.1}}) are a group of seven [[dehydrogenase]] [[enzyme]]s that occur in many organisms and facilitate the interconversion between [[alcohol]]s and [[aldehyde]]s or [[ketone]]s with the reduction of NAD<sup>+</sup> to NADH. In [[human]]s and many other [[animal]]s, they serve to break down alcohols which could otherwise be toxic; in [[yeast]] and many [[bacterium|bacteria]], some alcohol dehydrogenases [[catalysis|catalyze]] the opposite reaction as part of [[fermentation (food)|fermentation]]. The [[CAS number]] for this type of the enzyme is [9031-72-5]. ==Properties== Alcohol dehydrogenase is responsible for catalyzing alcohols into aldehydes and ketones, and vice versa. It does not work well with primary [[alcohols]]{{Dubious|date=March 2008}}. Instead, it works the best with secondary and cyclic alcohols. <ref>Sofer, W. and Martin, F. Presley. Annual Reviews. Analysis of Alcohol Dehydrogenase Gene Expression in Dysentary. 21 (1997):203-25.</ref> ===Oxidation of Alcohol=== ==Mechanism In Humans== Note: The mechanism in yeast and bacteria is the reverse of this reaction. ===Steps=== # Binding of the coenzyme NAD+; # Binding of the alcohol substrate by coordination to zinc; # Deprotonation of the His-51; # Deprotonation of nicotinamide ribose; # Deprotonation of Ser-48; # Deprotonation of the alcohol; # Hydride transfer from the [[alkoxide]] ion to NAD<sup>+</sup>, leading to NADH and a zinc bound aldehyde or ketone; # Release of the product aldehyde; These steps are supported through kinetic studies.<ref>Hammes-Schiffer, Sharon and Benkoviv, Stephen J. Relating Protein Motion to Catalysis. Annual Review of Biochemistry. 75(2006):519-41.</ref> <!-- Image with unknown copyright status removed: [[Image:thetotalmech3.gif]] --> ==Explanation== This is an example of the mechanism of liver alcohol dehydrogenase. The substrate is coordinated to the zinc and this enzyme has two zinc atoms per subunit. One is the active site, which is involved in catalysis. In the active site, the ligands are Cys-46, Cys-174,His-67 and one water molecule. The other subunit is involved with structure. In this mechanism, the hydride from the alcohol goes to NAD<sup>+</sup>. Crystal structures indicate that the His-51 deprotonates the nicotinamide ribose, which deprotonates Ser-48. Finally, Ser-48 deprotonates the alcohol, making it an aldehyde. <ref>Hammes-Schiffer, Sharon and Benkovic, Stephen J. Relating Protein Motion to Catalysis. Annual Review of Biochemistry. 75(2006):519-41.</ref> ==Active Site== [[Image:active site3.jpg|500px]] This is the active site of alcohol dehydrogenase. The active site consists of a zinc atom, His-67, Cys-174, Cys-46, Ser-48, His-51, Ile-269, Val-292, Ala-317, and Phe-319. The zinc coordinates the substrate(alcohol). The zinc is coordinated by Cys-146, Cys-174, and His-67. Phe-319, Ala-317, His-51, Ile-269 and Val-292 stabilize NAD<sup>+</sup> by forming [[hydrogen bonds]]. His-51 and Ile-269 form hydrogen bonds with the alcohols on nicotinamide ribose. Phe-319, Ala-317 and Val-292 from hydrogen bonds with the amide on NAD<sup>+</sup><ref>Hammes-Schiffer, Sharon and Benkoviv, Stephen J. Relating Protein Motion to Catalysis. Annual Review of Biochemistry. 75(2006):519-41</ref>. == In humans == In humans, it exists in multiple forms as a dimer and is encoded by at least seven different genes. There are five classes (I-V) of alcohol dehydrogenase, but the [[hepatic]] form that is primarily used in humans is class 1. Class 1 consists of A,B, and C subunits that are encoded by the genes ADH1A, ADH1B, and ADH1C<ref>Sultatos and et. Toxicological Sciences. ''Incorporation of the Genetic control of Alcohol Dehydrogenase into a Physiologically Based Pharmacokinetic Model for Ethanol in Humans''</ref> The enzyme is contained in the lining of the [[stomach]] and in the [[liver]]. It catalyzes the [[oxidation]] of [[ethanol]] to [[acetaldehyde]]: :CH<sub>3</sub>CH<sub>2</sub>OH + NAD<sup>+</sup> → CH<sub>3</sub>CHO + [[NADH]] + H<sup>+</sup> This allows the consumption of [[alcoholic beverage]]s, but its evolutionary purpose is probably the breakdown of alcohols naturally contained in foods or produced by [[bacterium|bacteria]] in the [[digestive tract]]. Others believe that its evolutionary purpose is involved in vitamin A metabolism, as alcohols are relatively 'empty' calories, providing no nutritional benefit. Alcohol dehydrogenase is also involved in the toxicity of other types of alcohol: for instance, it oxidizes [[methanol]] to produce [[formaldehyde]] and [[ethylene glycol]] to ultimately yield [[glycolic acid|glycolic]] and [[oxalic acid]]s. Humans have at least six slightly different alcohol dehydrogenases. All of them are [[dimer]]s (consist of two [[polypeptide]]s), with each dimer containing two [[zinc]] [[ion]]s Zn<sup>2+</sup>. One of those ions is crucial for the operation of the enzyme: it is located at the catalytic site and holds the [[hydroxyl]] group of the alcohol in place. Alcohol Dehydrogenase activity varies between men and women, and between populations from different areas of the world. For example, women are unable to process alcohol at the same rate as men because they do not express the Alcohol Dehydrogenase as highly. The level of activity may not only be dependent on level of expression but due to [[allele|allelic]] diversity among the population. These allelic differences have been linked to region of origin. For example, populations from Europe have been found to express an allele for the alcohol dehydrogenase gene that makes it much more active than those found in populations from Asia or the Americas. == In yeast and bacteria == Unlike humans, yeast and bacteria do not ferment glucose to lactate. Instead, they ferment it to ethanol and CO<sub>2</sub>. The overall reaction can be seen below. Glucose + 2ADP +2Pi --> 2 ethanol + 2CO<sub>2</sub> + 2ATP +2H<sub>2</sub>O <ref>Nelson, David L. and Cox, Michael M. Lehniger Principles of Biochemistry. New York:W.H. Freeman and Company, 2005; p 180.</ref> In [[yeast]] and many [[bacterium|bacteria]], alcohol dehydrogenase plays an important part in fermentation: [[pyruvate]] resulting from [[glycolysis]] is converted to acetaldehyde and [[carbon dioxide]], and the acetaldehyde is then reduced to ethanol by an alcohol dehydrogenase called ADH1. The purpose of this latter step is the regeneration of NAD+, so that the energy-generating glycolysis can continue. Humans exploit this process to produce alcoholic beverages, by letting yeast ferment various fruits or grains. It is interesting to note that yeast can produce and consume their own alcohol. The main alcohol dehydrogenase in yeast is larger than the human one, consisting of four rather than just two subunits. It also contains zinc at its catalytic site. Together with the zinc-containing alcohol dehydrogenases of animals and humans, these enzymes from yeasts and many bacteria form the family of "long-chain"-alcohol dehydrogenases. [[Brewer's yeast]] also has another alcohol dehydrogenase, ADH2, which evolved out of a duplicate version of the chromosome containing the ADH1 gene. ADH2 is used by the yeast to convert ethanol back into acetaldehyde, and it is only expressed when sugar concentration is low. Having these two enzymes allows yeast to produce alcohol when sugar is plentiful (and this alcohol then kills off competing microbes), and then continue with the oxidation of the alcohol once the sugar, and competition, is gone.[http://www.newscientist.com/channel/life/mg19225831.100-festive-special-the-brewers-tale.html] Alcohol Dehydrogenase from Brewer's Yeast can be easily purified as follows: Using a 25 mM Pyrophosphate Buffer containing 5 mM Zinc Chloride, 5 mM EDTA, and 0.5 mg/ml BSA, disrupt yeast cells with a bead mill. Perform an ammonium sulfate precipitation at 40%, and discard the pellet. Perform a second ammonium sulfate precipitation at 70%, resuspend the resulting pellet in 1 ml of buffer. Run on a [[Sephadex]] G-100 column; ADH will elute in first few fractions. The sample can then be concentrated with a high concentration of ammonium sulfate as there should be few other proteins present. == Iron-containing alcohol dehydrogenases == A third family of alcohol dehydrogenases, unrelated to the above two, are [[iron]]-containing ones. They occur in bacteria, and an (apparently inactive) form has also been found in yeast<sup>[citation needed]</sup>. In comparison to enzymes the above families, these enzymes are oxygen-sensitive. == Other alcohol dehydrogenase types == A further class of alcohol dehydrogenases belongs to quinoenzymes and requires quinoid cofactors (e. g., pyrroloquinoline quinone, PQQ) as enzyme-bound electron acceptors. A typical example for this type of enzyme is methanol dehydrogenase of methylotrophic bacteria. == Applications == In fuel cells: Alcohol dehydrogenases can be used to catalyze the breakdown of fuel for an ethanol [[fuel cell]]. Scientists at [[Saint Louis University]] used carbon-supported alcohol dehydrogenase with poly([[methylene green]]) as an anode, with a [[nafion]] membrane, to achieve about 50 μ[[ampere|A]]/cm² [http://www.rsc.org/Publishing/Journals/LC/article.asp?doi=b412719f]. In biotransformation: Alcohol dehydrogenases are often used for the synthesis of enantiomerically pure stereoisomers of chiral alcohols. In contrast to the chemical process, the enzymes yield directly the desired enatiomer of the alcohol by reduction of the corresponding ketone. ==Health Issues== ===Alcoholism=== There have been studies showing that ADH may have an influence on the dependence on ethanol metabolism in alcoholics. Researchers have tentatively detected a few genes to be associated with alcoholism. If the variants of these genes encode slower metabolizing forms of ADH2 and ADH3, there is increased risk of alcoholism. The studies have found that mutations of ADH2 and ADH3 are related to alcoholism in Asian populations. However, research continues in order to identify the genes and their influence on alcoholism.<ref>Sher, Kenneth J., Grekin, Emily R., and Williams, Natalie A. The Development of Alcohol Use Disorders. Annual Review Clinical Psych. 1 (2005):493-523.</ref> ===Drug Dependence=== Drug dependence is another problem associated with ADH, which researchers think might be linked to alcoholism. One particular study suggests that drug dependence has seven ADH genes associated with it. These results may lead to treatments that target these specific genes. However, more research is necessary.<ref>Luo and et. Oxford Journals. Multiple ADH genes modulate risk for drug dependence in African- and European-Americans</ref> == See also == * [[Oxidoreductase]] * [[Ethanol]] ==References== {{reflist|1}} {{Enzyme references|EC_number=1.1.1.1|IUBMB_EC_number=1/1/1/1}} == External links == * [http://www.biochem.ucl.ac.uk/bsm/enzymes/ec1/ec01/ec01/ec0001/index.html PDBsum] has links to three-dimensional structures of various alcohol dehydrogenases contained in the [[Protein Data Bank]] * [http://www.expasy.org/cgi-bin/nicezyme.pl?1.1.1.1 ExPASy] contains links to the alcohol dehydrogenase sequences in [[Swiss-Prot]], to a [[Medline]] literature search about the enzyme, and to entries in other databases. * [http://www.brenda.uni-koeln.de/php/result_flat.php3?ecno=1.1.1.1 BRENDA] most comprehensive compilation of information and literature references about the enzyme; requires payment for commercial users * [http://www.epotential.com/radiofreegenome Radio Free Genome] created a musical score from a sequence of alcohol dehydrogenase. MP3 audio version and an open source version of the software used to create it is available. {{GO code links|GO_code=0004022|name=alcohol dehydrogenase}} {{Alcohol oxidoreductases}} [[Category:EC 1.1.1]] [[Category:NADH-dependent enzymes]] [[Category:Iron enzymes]] [[Category:Zinc enzymes]] [[bg:Алкохолдехидрогеназа]] [[de:Alkoholdehydrogenase]] [[fi:Alkoholidehydrogenaasi]] [[it:Alcol deidrogenasi]] [[ja:アルコールデヒドロゲナーゼ]] [[nl:Alcoholdehydrogenase]] [[pl:Dehydrogenaza alkoholowa]] [[ru:Алкогольдегидрогеназа]] [[sk:Alkoholdehydrogenáza]] [[sl:Alkohol-dehidrogenaza]] [[sv:Alkoholdehydrogenas]] [[zh:醇脫氫酶]]