Abstract
The level of glutamine synthetase in Micrococcus glutamicus ATCC1 3032 varied in response to the nitrogen source in culture medium; it was 10-20 fold higher in glutamate-, peptone- or yeast extract-grown cells than in ammonia-or urea-grown cells. Ammonia(3 mM)reduced the enzyme level to 50% when added to glutamate medium. No difference between nitrogen sources was observed in extent of inhibition by Mg2+ of γ-glutamylhydroxamate-forming (transferring) reaction in crude extracts.
The optimum pH was 7.0-8.0 for glutamine-forming (synthesizing) reaction and 7.0 for transferring reaction. The enzyme was stable to heating at 50°C for 10 min in 0.05M potassium phosphate buffer (pH 6.0) containing 0.1mM MnCl2. Km values for glutamate, ammonia and ATP in synthesizing reaction were 7.9, 5.0 and 1.2 mM, respectively. GTP and hydroxylamine could be substituted for ATP and ammonia with about 10 and 30% reactivity. Mg2+ was effective as a cofactor in synthesizing reaction and Mn2+ showed 34% of the reactivity of Mg2+ at a concentration of 30 mM. Glutamine synthetase was inhibited by adenosine, AMP and ADP but not by amino acids other than D-threonine. The regulation system of glutamine synthetase in M. glutamicus is discussed.
