Comparing Short-Term Effects of Ammonia and Methylamine on Nitrogenase Activity in Anabaena variabilis (ATCC 29413)

Cyanobacterium . Anabaena variabilis, Nitrogenase Regulation, Ammonia, Methylamine Using the heterocystous cyanobacterium A nabaena variabilis (ATCC 29413) in an alkaline environment its nitrogenase activity is rapidly inhibited by ammonia and methylamine. Nitrogenase inhibition by ammonia is probably caused by a mechanism comparable to the switch-off effect, which has been described for several species of the Rhodospirillaceae, whereas methyl-amine-induced inhibition is caused by an uncoupling effect only. Evidence for these different effects is obtained by comparing nitrogenase activity in cell-free extracts of filaments pretreated by ammonia or methylamine. In addition, ammonia-dependent nitrogenase inhibition is shown to be dependent on protein synthesis and on light intensity.