ATP Hydrolysis and Energy Transduction by Nitrogenase

Abstract

We have, in the past, described the functioning of molybdenum nitrogenase in terms of a kinetic model that describes the interactions between the two component proteins (the Fe-protein and the MoFe-protein), reductant dithionite, substrates and products (Lowe, Thorneley, 1984a,b; Thorneley, Lowe, 1983, 1984a,b). In this cycle ATP hydrolysis is associated with electron transfer from Kp2 to Kpl followed by obligate, rate-limiting, dissociation of the protein complex to give reduced Kpl and free oxidised Kp2_ox(MgADP)₂. Phosphate release was arbitrarily assigned to the protein complex dissociation step. Eight Fe-protein cycles, each involving the transfer of an electron to the MoFe-protein, combine to give a single MoFe-protein cycle in which a molecule of dinitrogen and eight protons are reduced to two molecules of ammonia and one of dihydrogen. The rates of all the partial reactions involved in these reactions have been independently measured.