Substrate-dependent, Thiol-dependent, Inactivation of Pig Brain Nicotinamide Adenine Dinucleotide Glycohydrolase

In the presence of NAD+ or NADH, microsomal pig brain NAD glycohydrolase is rapidly inactivated by dilute solutions of reduced dithiothreitol and other thiols. The rate of inactivation is increased by increased concentration of thiol, nicotinamide nucleotide, and increased values of pH. The inactive form of the enzyme is not reactivated by removal or destruction of the thiol. Inactivation of the enzyme is accompanied by an increase in the content of protein sulfhydryl groups as measured by reactivity toward 5,5'-dithiobis(2nitrobenzoic acid). These data together with analysis of the kinetics of the inactivation process suggest that inactivation is the consequence of the reduction of an essential protein disulfide group which is exposed to the aqueous environment following binding of a nicotinamide nucleotide coenzyme.