Alcohol dehydrogenase (EC 1.1.1.1) (ADH) catalyzes the reversible oxidation of ethanol to acetaldehyde with the concomitant reduction of NAD [1]. Currently three, structurally and catalytically, different types of alcohol dehydrogenases are known:

• Zinc-containing 'long-chain' alcohol dehydrogenases.
• Insect-type, or 'short-chain' alcohol dehydrogenases.
• Iron-containing alcohol dehydrogenases.

Zinc-containing ADH's [2,3] are dimeric or tetrameric enzymes that bind two atoms of zinc per subunit. One of the zinc atom is essential for catalytic activity while the other is not. Both zinc atoms are coordinated by either cysteine or histidine residues; the catalytic zinc is coordinated by two cysteines and one histidine. Zinc-containing ADH's are found in bacteria, mammals, plants, and in fungi. In most species there are more than one isozyme (for example, human have at least six isozymes, yeast have three, etc.). A number of other zinc-dependent dehydrogenases are closely related to zinc ADH [4], these are:

• Xylitol dehydrogenase (EC 1.1.1.9) (D-xylulose reductase).
• Sorbitol dehydrogenase (EC 1.1.1.14).
• Aryl-alcohol dehydrogenase (EC 1.1.1.90) (benzyl alcohol dehydrogenase).
• L-threonine 3-dehydrogenase (EC 1.1.1.103).
• Cinnamyl-alcohol dehydrogenase (EC 1.1.1.195) (CAD) [5]. CAD is a plant enzyme involved in the biosynthesis of lignin.
• Galactitol-1-phosphate 5-dehydrogenase (EC 1.1.1.251).
• Escherichia coli L-idonate 5-dehydrogenase (EC 1.1.1.264).
• Pseudomonas putida 5-exo-alcohol dehydrogenase (EC 1.1.1.-) [6].
• Escherichia coli starvation sensing protein rspB.
• Escherichia coli hypothetical protein yjgB.
• Escherichia coli hypothetical protein yjgV.
• Escherichia coli hypothetical protein yjjN.
• Yeast hypothetical protein YAL060w (FUN49).
• Yeast hypothetical protein YAL061w (FUN50).
• Yeast hypothetical protein YCR105w.

The pattern that we developed to detect this class of enzymes is based on a conserved region that includes a histidine residue which is the second ligand of the catalytic zinc atom.

This family also includes NADP-dependent quinone oxidoreductase (EC 1.6.5.5), an enzyme found in bacteria (gene qor), in yeast and in mammals where, in some species such as rodents, it has been recruited as an eye lens protein and is known as zeta-crystallin [7]. The sequence of quinone oxidoreductase is distantly related to that other zinc-containing alcohol dehydrogenases and it lacks the zinc-ligand residues. The torpedo fish and mammlian synaptic vesicle membrane protein vat-1 is realted to qor. We have developed a specific pattern for this subfamily.