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 Ca²⁺ at 1 m m but not at 0.1 m m. The concentration of intracellular Ca²⁺ was relatively high in the presence of these pesticides when 1 m m Ca²⁺ was also present, indicating that intracellular Ca²⁺ may participate in protecting nitrogenase activity against Methylparathion and Benthiocarb.