A role for nicotinamide adenine dinucleotide glycohydrolase in the control of glyceraldehyde-3-phosphate dehydrogenase activity.

Tumor nicotinamide adenine dinudeotide (NAD) glycohydrolase (EC.3.2.2.5) was purified 500-fold, and this preparation was used to study the influence of NAD glycohydrolase on the NAD + content and activity of crystalline glyceraldehyde-3phosphate dehydrogenase. The pseudomonomolecular velocity constant, k, for the hydrolysis of free NAD + was 5-fold that of the constant for the enzyme-bound NAD +. Hydrolysis of 90 percent or more of the bound NAD + did not result in a shift in the absorption spectrum of the dehydrogenase, which has a maximum at 276 m/a, or in a loss in enzyme activity. Native rabbit muscle glyceraldehyde-3-phosphate dehydrogenase was resistant to tryptic digestion but was rapidly inactivated by trypsin after hydrolysis of the bound NAD + by NAD glycohydrolase. Complete protection against such inactivation in the simultaneous presence of NAD glycohydrolase and trypsin was conferred by excess NAD +. It is suggested that increased NAD glycohydrolase activity may influence the level of NAD-dependent dehydrogenases in tissues containing proteolytic enzymes.