ISOLATION, PURIFICATION, AND SOME KINETIC-PROPERTIES OF MODERATELY ADENYLATED GLUTAMINE-SYNTHETASE FROM AZOSPIRILLUM-BRASILENSE-SP-245

The glutamine synthetase of the associative nitrogen-fixating microorg anism Azospirillum brasilense sp. 245 was purified by a procedure whic h includes treatment with DNase I and streptomycin sulfate, ammonium s ulfate fractionation, heat treatment, chromatography on DEAE-Toyopearl 650 M, and high performance liquid chromatography on Mono Q. The mode rately adenylated enzyme (n = 6.4) is electrophoretically homogenous. In the presence of Mn2+ or Mg2+ as the activating ion, the pH optimum for the biosynthetic reaction is 6.25 or 8.0, respectively. In the pre sence of Mg2+ the kinetic behavior of for the moderately adenylated Az ospirillum glutamine synthetase does not follow Michaelis-Menten kinet ics due to substrate inhibition by excess of both substrates, ammonium and glutamate. The K-m values for ammonium and glutamate are 0.2 and 2.3 mM, respectively.