Three topics related to the problem of energy transduction for nitrogen fixation are addressed. (1) the role(s) of the fixABC and dct genes necessary for nitrogen fixation in Rhizobium and Azotobacter vinelandii. Mutants will be constructed and the physiological and biochemical effects and N2-fixation by Mo, V and Fe-nitrogenases determined. (2) the detailed biochemistry of intermediates involved in the coupling of ATP hydrolysis to electron transfer and substrate reduction by nitrogenase. (3) chemical, spectroscopic and electrochemical techniques will be applied to studies on the redox behaviour of the 'P' clusters in MoFe proteins to attempt to elucidate the structure and function of these clusters.