The X-ray structure of the nitrogenase MoFe protein has established the organization and architecture of its multimetallic cofactors, the P-cluster (Fe8S7-8) and the FeMo-cofactor (MoFe7S9:homocitrate). Nonetheless, until recently it has not been possible to detect or characterize a substrate or inhibitor interacting with the functioning enzyme. In the present study we have used 57Fe ENDOR to study the CO-inhibited turnover states of a novel suite of 56,57Fe isotopomers of the MoFe protein, including those in which these two clusters are selectively, as well as uniformly, labeled. CO-inhibited MoFe protein exhibits two distinct EPR signals, one under low and another under high CO pressure. The 57Fe measurements, along with an earlier 13C ENDOR study of bound 13CO (Pollock, R.C.; Lee, H.I.; Cameron, L.M.; DeRose, V.J.; Hales, B.J.; Orme-Johnson, W.H.; Hoffman, B.M.J. Am. Chem. Soc. 1995, 117, 8686-8687), show that the two EPR signals arise from CO-bound FeMo-cofactor, in one case with one bound CO and in the other with two bound CO, and they further provide initial insights into the properties of the inhibitor-bound cluster.
ASJC Scopus subject areas
- Colloid and Surface Chemistry