Role of calcium in the inhibition of nitrogenase activity by Methylparathion and Benthiocarb in the cyanobacterium Nostoc muscorum.

Methylparathion and Benthiocarb inhibition of N2 fixation in the cyanobacterium Nostoc muscorum was reversed by Ca(2+) at 1 mM but not at 0.1 mM. The concentration of intracellular Ca(2+) was relatively high in the presence of these pesticides when 1 mM Ca(2+) was also present, indicating that intracellular Ca(2+) may participate in protecting nitrogenase activity against Methylparathion and Benthiocarb.