Towards the activation of nitrogenase by artificial reduction schemes

1. Towards the activation of nitrogenase by artificial reduction schemes F. Akif Tezcan, Department of Chemistry and Biochemistry, UCSD, La Jolla , CA 92093 Mechanistic details of how nitrogenase accomplishes the conversion of dinitrogen into ammonia still remain a mystery after decades of extensive research. Reduction of the nitrogenase active site metal cluster, the iron–molybdenum cofactor (FeMoco), is postulated to be requiredfor substrate binding and has only been achieved under turnover conditions in solution. We aim here to develop photochemical methods to activate FeMoco for substrate activation. We have succeeded in labeling 3 variants of molybdenum-iron protein (MoFeP) with Ru-based photo-active groups that are Cys-specific. These variants (wild-type, α-H196C, α-L158C) present Cys residues at three different distances from FeMoco and should produce different levels of electronic coupling to the active site. We determined that Ru-photosensitizers are located on the α-subunit of all three variants as desired, although their exact positions remain to be elucidated. Our initial photoreduction experiments (see left) have not shown significant amounts of substrate reduction. This may either indicate that 2-electron reduction schemes have to be devised or that the natural redox partner of MoFeP, the Fe-protein, is absolutely necessary for the activation of substrate reduction.