Introduction Click to copy section linkSection link copied! Nitrogenases catalyze the reduction of dinitrogen (N2) to ammonia (NH3) at an organometallic cofactor active site, [Fe7S9M(μ6-C)], where M represents Mo, V, or Fe (M = Fe is depicted in Figure 1A). (1) In addition to N2, this family of enzymes can reductively protonate non-native substrates, such as carbon monoxide, acetylene, and cyanide.