Effect of lead on nitrogenase and enzymes of nitrogen assimilation in a cyanobacterium Nostoc muscorum.

ABSTRACT

Lead decreased the growth rates, total cell mass, heterocyst frequency, total cell protein, nitrogenase activity, glutamine synthetase (GS) and glutamate synthase (GOGAT) activities in Nmuscorum. However, lead at 0.01 and 10 micrograms ml-1 conc. enhanced nitrogenase as well as GS activity of the cells. On transfer to excess lead (100 micrograms ml-1), nitrogenase and GS activities ceased almost after 24 hr in the cyanobacterium. It is deduced that lead has a two step effect on stimulation and inhibition of metabolic activity at 0.01 and 10 micrograms ml-1 concentration and 0.1 and 100 micrograms ml-1 concentration respectively indicating a close interaction between nitrogen fixation and GS activity. However, GOGAT activity is an exception to this two step stimulation and inhibition process.