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.
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