Analysis of active sites for N2 and H+ reduction on FeMo-cofactor of nitrogenase

Dinitrogen (N-2) and proton (H+), which act as physiological substrates of nitrogenase, are reduced on FeMo-co of the MoFe protein. However, researchers have different opinions about their exact reduction sites. Nitrogenases were purified from the wild type (WT) and five mutants of Azotobacter vinelandii (Av), including Q alpha 191K, Hal 950, nifV(-), Q alpha 191 K/nifV(-) and Ha195Q/nifV(-); and the activities of these enzymes for N2 and H+ reduction were analyzed. Our results suggest that the Fe2 and Fe6, atoms closed to the central sulfur atom (S2B) within FeMo-co, are sites for N2 binding and reduction and the Mo atom of FeMo-co is the site for H+ reduction. Combining these data with further bioinformatical analysis, we propose that two parallel electron channels may exist between the [8Fe7S] cluster and FeMo-co.