Abstract
Nitrogenase catalyzes the reduction of N(2) to NH(3) at its active-site cofactor. Recent studies of the 'conventional' Mo-nitrogenase suggest a plausible involvement of all cofactor belt-S sites in catalysis. Here, we use analytical, enzymatic and spectroscopic methods to demonstrate the same dynamic belt-S mobilization by the 'alternative' V-nitrogenase during catalysis. Our results point to belt-S turnover as a common catalytic feature of the homologous Mo- and V-nitrogenases while identifying an activated, but N(2)-free conformation of the V-nitrogenase that bears great potential for facilitating future mechanistic explorations of the intriguing nitrogenase enzyme.