The genetics and biochemistry of the reversible ADP-ribosylation systems of Rhodospirillum rubrum and Azospirillum lipoferum

In 1949, Gest and Kamen observed nitrogen fixation by Rhodospirillum rubrum, as well as the inhibition of that activity by ammonium (5). While the specific mechanism of that inhibition, the ADP-ribosylation of dinitrogenase reductase, has been known for several years, it is only recently that we have gained some insight into the regulation of that process. The presence of such a reversible ADP-ribosylation system has also been established in Rhodobacter capsulatum (7) and Azospirillum spp. (6), while suggestive evidence exists for other photosynthetic diazotrophs as well as Azorhizobium caulinodans (see ref. 14 for a more extensive review).