title: Regulation of glutamine synthetase, aspartokinase, and total protein turnover in Klebsiella aerogenes.
abstract: When suspensions of Klebsiella aerogenes are incubated in a nitrogen-free medium there is a gradual decrease in the levels of acid-precipitable protein and of aspartokinase III (lysine-sensitive) and aspartokinase I (threonine-sensitive) activities. In contrast, the level of glutamine synthetase increases slightly and then remains constant. Under these conditions, the glutamine synthetase and other proteins continue to be synthesized as judged by the incorporation of [14C]leucine into the acid-precipitable protein fraction and into protein precipitated by anti-glutamine synthetase antibodies, by the fact that growth-inhibiting concentrations of chloramphenicol also inhibit the incorporation of [14C]leucine into protein and into protein precipitated by anti-glutamine synthetase antibody, and by the fact that chloramphenicol leads to acceleration in the loss of aspartokinases I and III and promotes a net decrease in the level of glutamine synthetase and its cross-reactive protein. The loss of aspartokinases I and III in cell suspensions is stimulated by glucose and is inhibited by 2,4-dinitrophenol. Glucose also stimulates the loss of aspartokinases and glutamine synthetase in the presence of chloramphenicol. Cell-free extracts of K. aerogenes catalyze rapid inactivation of endogenous glutamine synthetase as well as exogenously added pure glutamine synthetase. This loss of glutamine synthetase is not associated with a loss of protein that cross-reacts with anti-glutamine synthetase antibodies. The inactivation of glutamine synthetase in extracts is not due to adenylylation. It is partially prevented by sulfhydryl reagents, Mn2+, antimycin A, 2,4-dinitrophenol, EDTA, anaerobiosis and by dialysis. Following 18 h dialysis, the capacity of extracts to catalyze inactivation of glutamine synthetase is lost but can be restored by the addition of Fe2+ (or Ni2+) together with ATP (or other nucleoside di- and triphosphates. After 40-60 h dialysis Fe3+ together with NADH (but not ATP) are required for glutamine synthetase inactivation. The results suggest that accelerated protein degradation in cells exposed to nitrogen-limited conditions reflects the differential destruction of some proteins, including aspartokinases I and III, in order to sustain the biosynthesis of others such as glutamine synthetase. The loss of glutamine synthetase activity in cell-free extracts is likely mediated in part by mixed-function oxidation systems and could represent a 'marking' step in protein turnover.
authors.forename: R M
authors.initials: RM
authors.lastname: Fulks
authors.forename: E R
authors.initials: ER
authors.lastname: Stadtman
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000641:Ammonia / Q000494:pharmacology; D001222:Aspartate Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D011232:Chemical Precipitation; D002701:Chloramphenicol / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007120:Immunochemistry; D007711:Klebsiella pneumoniae / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D008670:Metals / Q000494:pharmacology; D009584:Nitrogen / Q000502:physiology; D010770:Phosphotransferases / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D008670:Metals; D002701:Chloramphenicol; D000641:Ammonia; D000255:Adenosine Triphosphate; D010770:Phosphotransferases; D001222:Aspartate Kinase; D005974:Glutamate-Ammonia Ligase; D005947:Glucose; D009584:Nitrogen