Table 1.

Classes of ADH and tissue/cell ADH expression based on information mainly from Human Protein Atlas.

Class	ADH Subunit	Tissue Expression	Cell Compartment	Substrates
I	ADH1A active in fetal life low in adults	MPES: liver LPES: duodenum, small intestine [30]	⮚PM ⮚cytosol [31]	⮚ethanol ⮚retinol ⮚other aliphatic alcohols ⮚hydroxysteroids ⮚lipid peroxidation products [27,28,29]
	ADH1B major role in ethanol oxidation	HPES: liver MPES: duodenum, small intestine LPES: cerebellum, oral mucosa, esophagus, stomach, rectum, gallbladder, kidney, urinary bladder, vagina, breast, heart muscle, appendix, tonsils [32]	⮚PM ⮚cytosol [33]
	ADH1C major role in ethanol oxidation	HPES: liver MPES: stomach, duodenum, small intestine, rectum, gallbladder, kidney, urinary bladder, epididymis, seminal vesicle, breast, appendix LPES: cerebellum, basal ganglia, hippocampus, colon, testis, vagina, fallopian tube, heart muscle, skeletal muscle, adipose tissue, spleen, lymph node, tonsil, bone marrow [34]	⮚PM ⮚cytosol [35]
II	ADH4	HPES: liver MPES: duodenum LPES: small intestine [36]	⮚nucleoplasm ⮚cytosol [37]	⮚retinol ⮚long chain omega-hydroxy fatty acids ⮚benzoquinones [38]
III	ADH5 ineffective in ethanol oxidation	HPES: liver, kidney, testis, epididymis, smooth muscle MPES: thyroid gland, adrenal gland, nasopharynx, bronchus, lung, oral mucosa, salivary gland, esophagus, stomach, duodenum, small intestine, colon, rectum, gallbladder, pancreas, urinary bladder, seminal vesicle, prostate, vagina, ovary, endometrium, cervix, heart muscle, skin, appendix LPES: cerebral cortex, hippocampus, parathyroid gland, fallopian tube, placenta, breast, tonsil [39]	⮚general cytoplasmic expression [40]	⮚long-chain primary alcohols ⮚S-hydroxymethyl-glutathione ⮚formaldehyde [40]
IV	ADH6 contains steroid hormone receptor binding site [41]	MPES: liver, gallbladder, duodenum, small intestine LPES: stomach, rectum, kidney [42]	⮚N/A, cytosol? [43]
V	ADH7 ineffective in ethanol oxidation	HPES: nasopharynx, bronchus, oral mucosa, esophagus MPES: stomach, tonsil LPES: colon [44]	⮚PM ⮚cytosol [45]	⮚retinol derivatives, dietary alcohols (2-hexenol, juniperic acid) [46]

Legend: HPES—high protein expression score, MPES—medium protein expression score, LPES—low protein expression score, PM—plasma membrane.