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Optimum temperature and pH of glutamine synthetase activity (E.C. 3.6.1.2.) of R. sphaeroides D-230 was 35°C and 6.8, respectively. The adenylated state of GS in R. sphaeroides D-230 was stabilized by addition of 0.2 mg/ml of cethyltrimethylammoniumbromide. Valine, histidine, proline, isoleucine, and lysine were good nitrogen source for the growth of R. sphaeroides D-230. The growth of k sphaeroides D-230 in N2, NaNO3 or NH4C1 as sole nitrogen source was lower than in any other culture conditions. GS activity was inhibited, more or less, by various amino acid. The relative inhibition rate of the enzyme by added 7 mM arginine, NH4C1, N2, and NaNO3 was 63.8%, 26.79%, 6.24%, and 10.64%, respectively. The hydrogen evolution of R. sphaeroides ?D-230 was higher in N-limited media than in any other culture conditions. The hydrogen evolution of R. sphaeroides D-230 grown in N-limited media was inhibited by 0.1 mM MSX, irreversible GS inhibitor. GS activity was completely inhibited by 1.0 mM MSX but ammonia released maximally at the same concentration of MSX. Ammonia release by added MSX was increased up to 1.0 mM MSX, but decreased above 1.0 mM MSX. It is probably due to inhibition of nitrogenase activity by MSX. Nitrogenase activity was not inhibited at low concentration of MSX. These results suggests that the inhibition of nitrogenase activity by ammonia is mediated by products of ammonia assimilation rather than by ammonia itself.
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