Metabolic regulation of nitrogen fixation in Rhodospirillum rubrum

Nitrogenase activity in Rhodospirillum rubrum is post-translationally regulated by DRAG (dinitrogenase reductase glycohydrolase) and DRAT (dinitrogenase reductase ADP-ribosylation transferase). When a sudden increase in fixed nitrogen concentration or energy depletion is sensed by the cells, DRAG is inactivated and DRAT activated. We propose that the regulation of DRAG is dependent on its location in the cell and the presence of an ammonium-sensing protein.