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 two types (E and S) coded by 2 separate genes at different loci. Belongs to the zinc-containing alcohol dehydrogenase family. Class-I subfamily.