INVERSE RELATIONSHIP OF THE DEHYDROGENASE AND ADP-RIBOSYLATION ACTIVITIES IN SODIUM-NITROPRUSSIDE-TREATED GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE IN COINCIDENTAL

Incubation of glyceraldehyde-3-phosphate dehydrogenase (GAPD) with sod ium nitroprusside (SNP) decreased its activity in concentration- and t ime-dependent fashion in the presence of a thiol compound, with DTT be ing more effective than GSH. Both forward and backward reactions were effected. Coinciding with this, HgCl2-sensitive labelling of the prote in by [P-32]NAD+ also increased, indicating the stimulation of ADP-rib osylation. Treatment with SNP of GAPD samples from rabbit muscle, shee p brain and yeast inactivated the dehydrogenase activity of the three, but only the mammalian proteins showed ADP-ribosylation activity. The SNP-modified protein of rabbit muscle GAPD, freed from the reagent by Sephadex filtration showed a concentration-dependent restoration of t he dehydrogenase activity on preincubation with DTT and GSH. Such thio l-treated preparations also gave increased ADP-ribosylation activity w ith DTT, and to a lesser extent with GSH. The SNP-modified protein was unable to catalyze this activity with the native yeast enzyme and nat ive and heat-inactivated muscle enzyme. It was possible to generate th e ADP-ribosylation activity in muscle GAPD, by an NO-independent mecha nism, on dialysis in Tris buffer under aerobic conditions, and on incu bating with NADPH, but not NADH, in muscle and brain, but not yeast, e nzymes. The results suggest that the inverse relationship of the dehyd rogenase and ADP-ribosylation activities is coincidental but not corre lated.