title: Inactivation of glutamine synthetases by an NAD:arginine ADP-ribosyltransferase.
abstract: Glutamine synthetase from ovine brain has a critical arginine residue at the catalytic site (Powers, S. G., and Riordan, J.F. (1975) Proc. Natl. Acad. Sci. U.S. A. 72, 2616-2620). This enzyme is now shown to be a substrate for a purified NAD:arginine ADP-ribosyltransferase from turkey erythrocyte cytosol that catalyzes the transfer of ADP-ribose from NAD to arginine and purified proteins. The transferase catalyzed the inactivation of the synthetase in an NAD-dependent reaction; ADP-ribose and nicotinamide did not substitute for NAD. Agmatine, an alternate ADP-ribose acceptor in the transferase-catalyzed reaction, prevented inactivation of glutamine synthetase. MgATP, a substrate for the synthetase which was previously shown to protect that enzyme from chemical inactivation, also decreased the rate of inactivation in the presence of NAD and ADP-ribosyltransferase. Using [32P]NAD, it was observed that approximately 90% inactivation occurred following the transfer of 0.89 mol of [32P]ADP-ribose/mol of synthetase. The erythrocyte transferase also catalyzed the NAD-dependent inactivation of glutamine synthetase purified from chicken heart; 0.60 mol of ADP-ribose was transferred per mol of enzyme, resulting in a 95% inactivation. As noted with the ovine brain enzyme, agmatine and MgATP protected the chicken synthetase from inactivation and decreased the extent of [32P]ADP-ribosylation of the synthetase. These observations are consistent with the conclusion that the NAD:arginine ADP-ribosyltransferase modifies specifically an arginine residue involved in the catalytic site of glutamine synthetase. Although the transferase can use numerous proteins as ADP-ribose acceptors, some characteristics of this particular arginine, perhaps the same characteristics that are involved in its function in the catalytic site, make it a favored ADP-ribose acceptor site for the transferase.
mesh_terms: D036002:ADP Ribose Transferases; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000376:Agmatine / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002417:Cattle; D004912:Erythrocytes / Q000201:enzymology; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors*; D007700:Kinetics; D009243:NAD / Q000378:metabolism; D010430:Pentosyltransferases / Q000378:metabolism*; D014422:Turkeys
chemical_list: D009243:NAD; D000376:Agmatine; D000255:Adenosine Triphosphate; D036002:ADP Ribose Transferases; D010430:Pentosyltransferases; D005974:Glutamate-Ammonia Ligase