Some properties of reactions catalyzed by pig brain NAD glycohydrolase

Abstract

Some aspects of pig brain NADase-catalyzed hydrolysis of NAD have been examined employing a partially purified enzyme and a titrimetric assay for enzyme activity. In accord with previous observations, this enzyme was observed to be catalytically active toward a number of NAD analogs and toward both NMN and nicotinamide nucleoside. It is subject to competitive inhibition by nicotinamide. Employing the natural substrate, the reaction velocity is observed to be rather insensitive to changes in pH, diminishing some fourfold as the pH is lowered from 9 to 4. The kinetic solvent deuterium isotope effect, V H2 o V D2 o , increases from 1.5 at pH 8.7 to 2.5 at pH 7.7. The pig brain NADase-catalyzed reaction is subject to marked inhibition by dithiothreitol resulting from rapid inactivation of the enzyme. Treatment of the inactivated enzyme with thiols has not resulted in reactivation of the enzyme.