LAUSR

Abstract Nitrogen is a crucial component of DNA, RNA and proteins, or the essential element that allows animals and plants to live and grow. Nevertheless, since most of the nitrogen in the atmosphere is unavailable for the life of many microorganisms, “nitrogenases” are enzymes specifically involved in the “biological nitrogen fixation”, or the catalytic reduction at ambient temperature of the inert atmospheric nitrogen to the metabolically useful ammonia. As a matter of fact such a catalytic process is the first step that triggers the complex system constituted by “the nitrogen cycle”. Based on their content in active metal-sulfur clusters nitrogenases are divided in MoFe, VFe and FeFe enzymes. Having in the last years systematically reviewed structure/electrochemistry of different classes of iron-sulfur clusters, we face now with structure/electrochemistry of the metal-sulfur components of the three types of nitrogenases expressed by different microorganisms.