Two mechanisms for the regulation of the nitrogenase Fe-protein activity have been described in Rhodobacter capsulatus. One involves the classical ADP-ribosylation process, whereas the second one is independent of ADP-ribosylation (Yakunin, Hallenbeck 1998). R. capsulatus contains two nifA genes and one an/A (see Masepohl et al. this volume). In this bacterium, a double glnB-glnK mutant escapes ammonia control both at the level of the synthesis of nitrogenase and the regulation of its activity. A review of the current situation was presented by Patrick Hallenbeck, who discussed the possible involvement of the PII and Amt proteins in the regulatory processes.
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