Glutamine synthetase from pv. was purified 500-fold. Maximum activity was observed with 10 mM-glutamate, 20mM-ATP and 4mM-NHCl. The enzyme exhibited substrate inhibition; higher levels of glutamate, Mg. ATP or NHCl decreased its activity. The γ-glutamyltransferase activity was inhibited by Mg (75% at 10mM-Mg). 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. , 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 y-glutamyltransferase activity of the enzyme if ADP was used in the assay, but did when ATP was used.


Article metrics loading...

Loading full text...

Full text loading...


Most cited this month Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error