ADP-RIBOSYLATION OF GLUTAMINE-SYNTHETASE IN THE CYANOBACTERIUM SYNECHOCYSTIS SP STRAIN PCC-6803

Glutamine synthetase (GS) inactivation was observed in crude cell extr acts and in the high-speed supernatant fraction from the cyanobacteriu m Synechocystis sp, strain PCC 6803 following the addition of ammonium ions, glutamine, or glutamate, Dialysis of the high-speed supernatant resulted in loss of inactivation activity, but this could be restored by the addition of NADH, NADPH, or NADP(+) and, to a lesser extent, N AD(+), suggesting that inactivation of GS involved ADP-ribosylation, T his form of modification was confirmed both by labelling experiments u sing [P-32]NAD(+) and by chemical analysis of the hydrolyzed enzyme, T hree different forms of GS, exhibiting no activity, biosynthetic activ ity only, or transferase activity only, could be resolved by chromatog raphy, and the differences in activity were correlated with the extent of the modification. Both biosynthetic and transferase activities wer e restored to the completely inactive form of GS by treatment with pho sphodiesterase.