O2-dependent nitrogenase switch-off in Rhodobacter capsulatus E1F1

Nitrogenase of Rhodobacter capsulatus E1F1 (formerly known as Rhodopseudomonas capsulata E1F1) was partially resistant to O2 inactivation in vivo. This inactivation was reversed by restoring anaerobic conditions, was independent from de novo protein synthesis and its extent was decreased upon preincubation of the cells with dioxygen at low pressures and also in the presence of H2. Illuminated cells exhibited a low rate of O2 uptake which was enhanced in the presence of H2, particularly in cells preincubated with O2. These results indicate that R. capsulatus E1F1 can develop for nitrogenase a protective system against dioxygen which, at least, consists of an uptake hydrogenase and an inducible electron transport system linked to a respiratory chain.