Name the most crucial enzyme found in root nodules for $N_2$ fixation. Does it require a special pink-coloured pigment for its functioning? Elaborate.

(N/A) The most crucial enzyme found in root nodules for $N_2$ fixation is Nitrogenase.
Nitrogenase is a Mo-Fe protein that catalyzes the conversion of atmospheric nitrogen $(N_2)$ into ammonia $(NH_3)$.
Yes,it requires a special pink-coloured pigment called leghaemoglobin for its functioning.
Nitrogenase is highly sensitive to molecular oxygen $(O_2)$.
Leghaemoglobin acts as an oxygen scavenger,creating an anaerobic (oxygen-free) environment within the root nodules,which is essential for the activity of the nitrogenase enzyme.