Role of the essential thiol groups of yeast alcohol dehydrogenase.

1. Yeast alcohol dehydrogenase inactivated by reaction with iodoacetamide retains 85% of the original NADH-binding capacity as measured under conditions of saturating coenzyme concentration. 2. The dissociation constant of the enzyme-NADH complex is unaffected by inactivation of the enzyme with iodoacetamide, and the affinity of the enzyme for NAD(+) and pyridine-3-aldehyde-adenine dinucleotide (PAAD(+)) appears to be similarly unaffected. 3. Enzyme inactivated with iodoacetamide has lost the ability to form normal ternary complexes of the type enzyme-NADH-acetamide and enzyme-PAAD(+)-hydroxylamine that are characteristic of the native enzyme.