Coenzyme binding in alcohol dehydrogenase

Crystallographic investigations of horse liver alcohol dehydrogenase have demonstrated that NAD is not a passive participant in the redox reactions catalysed by the enzyme. On the molecular level NAD acts as an activator which induces an active form of the enzyme. This is mediated by a large conformational change, making the active site dehydrated and by providing one part of the substrate-binding cleft. The catalytic events, substrate binding, inhibitor binding and the role of the catalytic zinc ion are discussed in relation to the role of NAD. Human alcohol dehydrogenase isoenzymes which have very different substrate specificities are discussed in relation to sequence differences.