For its action, nitrogenase requires

The enzyme nitrogenase is a Mo-Fe protein and catalyses the conversion of atmospheric $\mathrm{N}_2$ to $\mathrm{NH}_3$ as $$\begin{aligned} \mathrm{N}_2+8 e^{-}+8 \mathrm{H}^{+}+16 \mathrm{ATP} \longrightarrow & 2 \mathrm{NH}_3+\mathrm{H}_2 \\ + & 16 \mathrm{ADP}+16 \mathrm{P}_{\mathrm{i}} \end{aligned}$$ Enzyme nitrogenase functions under anaerobic condition and the pigment leghaemoglobin protect it from oxygen.