Human alcohol dehydrogenase. ADH is a homodimer. Each monomer has 374 residues with molecular weight of 74000 dalton. There are two domains. The NAD+-binding domain (residues 176-318) is a central beta-sheet of 6 strands flanked by alpha helices. NAD+ binds to the C-terminus of the beta-sheet. The catalytic domain (residues 1-175, 319-374) also has a alpha/beta structure. The inter-domain interface forms a cleft which contains the active catalytic site. The interface is formed by two helices, one from each domain crossing over each other. There are two Zn++ cations per monomer, one at the catalytic site being mandatory for catalysis. The alcohol substrate binds inside the cleft where the Zn++ cation is, whilst the nicotinamide ring of the NAD finds its way pointing into the cleft. The dimer forms with the two NAD-binding domains packing together such that their 2 central beta sheets combine to form a 12-stranded beta sheet. The catalytic domains are situated at opposite ends.