title: The stereochemistry and dynamics of the introduction of hydrogen atoms onto FeMo-co, the active site of nitrogenase.
abstract: The catalyzed hydrogenations effected at the active site FeMo-co of nitrogenase have been proposed to involve serial supply of the required multiple protons along a proton wire terminating at sulfur atom S3B of FeMo-co. In conjunction with serial electron transfer to FeMo-co, these protons become H atoms, and then are able to migrate from S3B to other Fe and S atoms of FeMo-co, and to transfer to bound substrate and intermediates. This general model, which can account for all reactions of nitrogenase, involves a preparatory stage in which each incoming H atom is required to move from the proton delivery side of S3B to the opposite migration side of S3B. This report examines the mechanism of this reconfiguration of S3B-H, finding four stable configurations in which S3B-H has pyramidal-trigonal coordination, with one elongated Fe-S3B interaction. The transition states and energies for reconfiguration are described. Pseudotetrahedral four coordination and planar-trigonal coordination for S3B-H are less stable than pyramidal-trigonal coordination. Results are presented for FeMo-co with one, two, three, and four H atoms (the E1H1, E2H2, E3H3, and E4H4 Thorneley-Lowe stages), and the general principles are defined, for application in the various chemical mechanisms of nitrogenase.
authors.affiliation: School of Chemistry, University of New South Wales , Sydney 2052, Australia.
authors.forename: Ian
authors.initials: I
authors.lastname: Dance
mesh_terms: D016948:Azotobacter vinelandii / Q000737:chemistry / Q000201:enzymology*; D020134:Catalytic Domain; D006859:Hydrogen / Q000737:chemistry*; D008958:Models, Molecular; D009591:Nitrogenase / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D006859:Hydrogen; D009591:Nitrogenase