The thiol groups of yeast alcohol dehydrogenase

Abstract

The reactions of yeast alcohol dehydrogenase with iodoacetamide, iodoacetate and p-chloromercuribenzoate were investigated. One thiol group/catalytic site reacted much faster than all the others with iodoacetamide. The reaction of the enzyme with iodoacetamide was first-order with respect to the concentration of each component and independent of pH between pH 4 and 10. NADH protected the enzyme more strongly than NAD+ from inactivation by iodoacetamide and iodoacetate. The binding constants for the coenzymes were calculated from protection data. Acetaldehyde enhanced, and ethanol had no effect on, the inactivation of the enzyme by iodoacetamide and iodoacetate. The results are consistent with the theory proposed by Rabin and Whitehead (1962) for the mode of action of this enzyme.