%0 Journal Article %A THOMAS, MICHAEL D. %A DURBIN, RICHARD D. %T Glutamine Synthetase from Pseudomonas syringae pv. tabaci: Properties and Inhibition by Tabtoxinine-β-lactam %D 1985 %J Microbiology, %V 131 %N 5 %P 1061-1067 %@ 1465-2080 %R https://doi.org/10.1099/00221287-131-5-1061 %I Microbiology Society, %X Glutamine synthetase from Pseudomonas syringae pv. tabaci was purified 500-fold. Maximum activity was observed with 10 mm-glutamate, 20 mm-ATP and 4 mm-NH4Cl. The enzyme exhibited substrate inhibition; higher levels of glutamate, Mg. ATP or NH4Cl decreased its activity. The γ-glutamyltransferase activity was inhibited by Mg2+ (75% at 10mm-Mg2+). The enzyme was heat stable and there appeared to be only one form present. Tabtoxinine-β-lactam, a hydrolytic product of tabtoxin produced by pv. tabaci, inactivated the enzyme. This inhibition was linear with respect to the concentration of the inhibitor, and enzyme activity could not be recovered by dialysis, acetone precipitation or incubation with crude cell lysate. Mg. ATP and ammonium ions were required for binding of the inhibitor: incubation of tabtoxinine-β-lactam with the enzyme in the presence of both Mg. ATP and ammonium ions resulted in a greater decrease in synthetase activity than incubation with either one or neither component. Tabtoxinine-β-lactam did not inhibit the γ-glutamyltransferase activity of the enzyme if ADP was used in the assay, but did when ATP was used. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-131-5-1061