On the reduced and oxidized forms of the FeMo- cofactor of Azotobacter vinelandii nitrogenase

Reduced and oxidized forms of the FeMo- cofactor of Azotobacter vinelandii nitrogenase are examined theoretically within the intermediate neglect of differential overlap model. The results obtained favor one of the experimentally suggested modes of contraction of the metal system which results in an expansion of the central cavity of the cofactor. The bond index analysis indicates marked changes in the Mo coordination upon electron addition which may contribute to an opening of the Mo atom as a possible binding site at the advanced stages of the reduction process. In this work we also compare the 39- and 41-electron [MoFe₇] core as possible native resting states, both compatible with known spin and M?ssbauer spectroscopies. Received: 19 March 1997 / Accepted: 8 May 1997