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.

Iron-containing ADH's have been found in yeast (gene ADH4) [2], as well as in Zymomonas mobilis (gene adhB) [3]. These two iron-containing ADH's are closely related to the following enzymes:

• Escherichia coli propanediol oxidoreductase (EC 1.1.1.77) (gene fucO) [4], an enzyme involved in the metabolism of fucose and which also seems to contain ferrous ion(s).
• Clostridium acetobutylicum NADPH- and NADH-dependent butanol dehydrogenases (EC 1.1.1.-) (genes adh1, bdhA and bdhB) [5], an enzyme which has activity using butanol and ethanol as substrates.
• Escherichia coli adhE [6], an iron-dependent enzyme which harbor three different activities: alcohol dehydrogenase, acetaldehyde dehydrogenase (acetylating) (EC 1.2.1.10) and pyruvate-formate-lyase deactivase.
• Bacterial glycerol dehydrogenase (EC 1.1.1.6) (gene gldA or dhaD) [7].
• Clostridium kluyveri NAD-dependent 4-hydroxybutyrate dehydrogenase (4hbd) (EC 1.1.1.61).
• Citrobacter freundii and Klebsiella pneumoniae 1,3-propanediol dehydrogenase (EC 1.1.1.202) (gene dhaT).
• Bacillus methanolicus NAD-dependent methanol dehydrogenase (EC 1.1.1.244) [8].
• Escherichia coli and Salmonella typhimurium ethanolamine utilization protein eutG.
• Escherichia coli hypothetical protein yiaY.
• Escherichia coli hypothetical protein ybdH.
• Escherichia coli hypothetical protein yqhD.
• Methanococcus jannaschii hypothetical protein MJ0712.

The patterns that we developed to detect this class of enzymes are based on two conserved regions.