Editing Alcohol dehydrogenase (section)

=== Human ===
In humans, ADH exists in multiple forms as a [[Dimerization (chemistry)|dimer]] and is encoded by at least seven genes. Among the five classes (I-V) of alcohol dehydrogenase, the [[hepatic]] forms that are used primarily in humans are class 1. Class 1 consists of α, β, and γ subunits that are encoded by the genes [[ADH1A]], [[ADH1B]], and [[ADH1C]].<ref name="pmid14718645">{{cite journal | vauthors = Sultatos LG, Pastino GM, Rosenfeld CA, Flynn EJ | title = Incorporation of the genetic control of alcohol dehydrogenase into a physiologically based pharmacokinetic model for ethanol in humans | journal = Toxicological Sciences | volume = 78 | issue = 1 | pages = 20–31 | date = March 2004 | pmid = 14718645 | doi = 10.1093/toxsci/kfh057 | doi-access =  }}</ref><ref>{{cite journal | vauthors = Edenberg HJ, McClintick JN | title = Alcohol Dehydrogenases, Aldehyde Dehydrogenases, and Alcohol Use Disorders: A Critical Review | journal = Alcoholism: Clinical and Experimental Research | volume = 42 | issue = 12 | pages = 2281–2297 | date = December 2018 | pmid = 30320893 | doi = 10.1111/acer.13904 | pmc = 6286250 }}</ref> The enzyme is present at high levels in the [[liver]] and the lining of the [[stomach]].<ref name="Farrés">{{cite journal | vauthors = Farrés J, Moreno A, Crosas B, Peralba JM, Allali-Hassani A, Hjelmqvist L, Jörnvall H, Parés X | display-authors = 6 | title = Alcohol dehydrogenase of class IV (sigma sigma-ADH) from human stomach. cDNA sequence and structure/function relationships | journal = European Journal of Biochemistry | volume = 224 | issue = 2 | pages = 549–57 | date = September 1994 | pmid = 7925371 | doi = 10.1111/j.1432-1033.1994.00549.x | doi-access =  }}</ref> It catalyzes the [[oxidation]] of [[ethanol]] to [[acetaldehyde]] (ethanal):

: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 [[bacteria]] in the [[digestive tract]].<ref name="urlwww.medicinenet.com">{{cite web | url = http://www.medicinenet.com/alcohol_and_nutrition/article.htm | title = Alcohol and Nutrition | vauthors = Kovacs B, Stöppler MC | publisher = MedicineNet, Inc. | access-date = 2011-06-07 | archive-url = https://web.archive.org/web/20110623122224/http://www.medicinenet.com/alcohol_and_nutrition/article.htm | archive-date = 23 June 2011 | url-status = dead }}</ref>

Another evolutionary purpose is reversible metabolism of [[retinol]] ([[vitamin A]]), an alcohol, to [[retinaldehyde]], also known as retinal, which is then irreversibly converted into [[retinoic acid]], which regulates expression of hundreds of genes.<ref name="Duester">{{cite journal | vauthors = Duester G | title = Retinoic acid synthesis and signaling during early organogenesis | journal = Cell | volume = 134 | issue = 6 | pages = 921–31 | date = September 2008 | pmid = 18805086 | pmc = 2632951 | doi = 10.1016/j.cell.2008.09.002 }}</ref><ref>{{cite journal | vauthors = Hellgren M, Strömberg P, Gallego O, Martras S, Farrés J, Persson B, Parés X, Höög JO | title = Alcohol dehydrogenase 2 is a major hepatic enzyme for human retinol metabolism | journal = Cellular and Molecular Life Sciences | volume = 64 | issue = 4 | pages = 498–505 | date = February 2007 | pmid = 17279314 | doi = 10.1007/s00018-007-6449-8 | s2cid = 21612648 | pmc = 11138474 }}</ref><ref>{{cite book |vauthors=Blaner WS |title = Present Knowledge in Nutrition, Eleventh Edition |chapter = Vitamin A | veditors = Marriott BP, Birt DF, Stallings VA, Yates AA |publisher = Academic Press (Elsevier) |year=2020 |location = London, United Kingdom |pages = 73–92 |isbn=978-0-323-66162-1}}</ref>

{|
|-
|{{infobox protein
| Name = [[ADH1A|alcohol dehydrogenase 1A,<br />α polypeptide]]
| caption =
| image =
| width =
| HGNCid = 249
| Symbol = [[ADH1A]]
| AltSymbols = ADH1
| EntrezGene = 124
| OMIM = 103700
| RefSeq = NM_000667
| UniProt = P07327
| PDB =
| ECnumber = 1.1.1.1
| CAS_number=
| Chromosome = 4
| Arm = q
| Band = 23
| LocusSupplementaryData =
}}
|{{infobox protein
| Name = [[ADH1B|alcohol dehydrogenase 1B,<br />β polypeptide]]
| caption =
| image =
| width =
| HGNCid = 250
| Symbol = [[ADH1B]]
| AltSymbols = ADH2
| EntrezGene = 125
| OMIM = 103720
| RefSeq = NM_000668
| UniProt = P00325
| PDB =
| ECnumber = 1.1.1.1
| Chromosome = 4
| Arm = q
| Band = 23
| LocusSupplementaryData =
}}
|{{infobox protein
| Name = [[ADH1C|alcohol dehydrogenase 1C,<br />γ polypeptide]]
| caption =
| image =
| width =
| HGNCid = 251
| Symbol = [[ADH1C]]
| AltSymbols = ADH3
| EntrezGene = 126
| OMIM = 103730
| RefSeq = NM_000669
| UniProt = P00326
| PDB =
| ECnumber = 1.1.1.1
| Chromosome = 4
| Arm = q
| Band = 23
| LocusSupplementaryData =
}}
|}

Alcohol dehydrogenase is also involved in the toxicity of other types of alcohol: For instance, it oxidizes [[methanol]] to produce [[formaldehyde]] and ultimately [[formic acid]].<ref>{{cite book | vauthors = Ashurst JV, Nappe TM | chapter = Methanol Toxicity |date=2020 | chapter-url=http://www.ncbi.nlm.nih.gov/books/NBK482121/| title = StatPearls |place= Treasure Island (FL)|publisher=StatPearls Publishing|pmid=29489213|access-date=2020-11-06}}</ref> Humans have at least six slightly different alcohol dehydrogenases. Each is a [[protein dimer|dimer]] (i.e., consists 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. {{Citation needed|date=February 2022}}

Alcohol dehydrogenase activity varies between men and women, between young and old, and among populations from different areas of the world. For example, young women are unable to process alcohol at the same rate as young men because they do not express the alcohol dehydrogenase as highly, although the inverse is true among the middle-aged.<ref name="pmid12107043">{{cite journal | vauthors = Parlesak A, Billinger MH, Bode C, Bode JC | title = Gastric alcohol dehydrogenase activity in man: influence of gender, age, alcohol consumption and smoking in a caucasian population | journal = Alcohol and Alcoholism | volume = 37 | issue = 4 | pages = 388–93 | year = 2002 | pmid = 12107043 | doi = 10.1093/alcalc/37.4.388 | doi-access = free }}</ref> The level of activity may not be dependent only on level of expression but also on [[allele|allelic]] diversity among the population.

The human genes that encode class II, III, IV, and V alcohol dehydrogenases are [[ADH4]], [[ADH5]], [[ADH7]], and [[ADH6]], respectively.
<div style="overflow:auto;">
{|
|-
|{{infobox protein
| Name = [[ADH4|alcohol dehydrogenase 4<br />(class II), π polypeptide]]
| caption =
| image =
| width =
| HGNCid = 252
| Symbol = [[ADH4]]
| AltSymbols =
| EntrezGene = 127
| OMIM = 103740
| RefSeq = NM_000670
| UniProt = P08319
| PDB =
| ECnumber = 1.1.1.1
| Chromosome = 4
| Arm = q
| Band = 22
| LocusSupplementaryData =
}}
|{{infobox protein
| Name = [[ADH5|alcohol dehydrogenase 5<br />(class III), χ polypeptide]]
| caption =
| image =
| width =
| HGNCid = 253
| Symbol = [[ADH5]]
| AltSymbols =
| EntrezGene = 128
| OMIM = 103710
| RefSeq = NM_000671
| UniProt = P11766
| PDB =
| ECnumber = 1.1.1.1
| Chromosome = 4
| Arm = q
| Band = 23
| LocusSupplementaryData =
}}
|{{infobox protein
| Name = [[ADH6|alcohol dehydrogenase 6<br />(class V)]]
| caption =
| image =
| width =
| HGNCid = 255
| Symbol = [[ADH6]]
| AltSymbols =
| EntrezGene = 130
| OMIM = 103735
| RefSeq = NM_000672
| UniProt = P28332
| PDB =
| ECnumber = 1.1.1.1
| Chromosome = 4
| Arm = q
| Band = 23
| LocusSupplementaryData =
}}
|{{infobox protein
| Name = [[ADH7|alcohol dehydrogenase 7<br />(class IV), μ or σ polypeptide]]
| caption =
| image =
| width =
| HGNCid = 256
| Symbol = [[ADH7]]
| AltSymbols =
| EntrezGene = 131
| OMIM = 600086
| RefSeq = NM_000673
| UniProt = P40394
| PDB =
| ECnumber = 1.1.1.1
| Chromosome = 4
| Arm = q
| Band = 23
| LocusSupplementaryData = -q24 }}
|}</div>