MODIFICATION OF GLUTAMINE-SYNTHETASE IN STREPTOMYCES-GRISEUS BY ADP-RIBOSYLATION AND ADENYLYLATION

Addition of NH4+ to Streptomyces griseus 2682 cells grown in NO3-conta ining medium resulted in a rapid decline in glutamine synthetase activ ity due to covalent modification of the enzyme. The NH4+ promoted inac tivation of the enzyme was inhibited by the ADP-ribosyltransferase inh ibitor 3-methoxybenzamide. In the presence of ADP-ribosyltransferase a ctivity the purified glutamine synthetase was also inhibited by NAD(+) in a concentration-dependent manner. ADP-ribosylation of glutamine sy nthetase was demonstrated in vitro by showing the incorporation of lab eled ADP-ribose from [alpha-P-32]NAD(+) into glutamine synthetase subu nits. Beside ADP-ribosylation, adenylylation of glutamine synthetase w as also shown in S. griseus since phosphodiesterase I treatment reacti vated the enzyme in crude extracts of NH4+-shocked cells. Glutamine sy nthetase was also inhibited and modified by ATP in crude cellular extr acts. These results suggest that in S. griseus 2682 ADP-ribosylation o f glutamine synthetase could be an alternative modification to adenyly lation to regulate glutamine synthetase activity. (C) 1994 Academic Pr ess, Inc.