Glutamine synthetase and arginine inhibition of nitrate reductase activity in Anabaena cycadeae.

Wild-type Anabaena cycadeae with normal glutamine synthetase (GS) activity utilized arginine as sole N source whereas a mutant strain lacking GS activity did not. Nitrate reductase (NR) activity, higher in the mutant strain than the wild-type strain, was inhibited by arginine though arginine-dependent NH 4 (+) generation was higher in the mutant strain than in the wild-type. This suggests that (1) NR activity is NO inf3 (sup-) -inducible and arginine-repressible; and (2) while GS activity is required for the assimilation of arginine as sole N-source, it is not required for arginine inhibition of NR activity.