a primary alcohol + NAD(+) = an aldehyde + H(+) + NADH a secondary alcohol + NAD(+) = a ketone + H(+) + NADH Binds 2 Zn(2+) ions per subunit. Dimer of identical or non-identical chains of three types (A, B, C), which are coded by 3 separate genes at different loci. Belongs to the zinc-containing alcohol dehydrogenase family. Class-I subfamily.