title: Model studies for molybdenum enzymes. Reduction of cytochrome c complexes by mu-oxo-bis[oxodihydroxo(L-cysteinato)molybdate(V)].
abstract: The reduction by mu-oxo-bis[oxodihydroxo(L-cysteinato)molybdate(V)] (I) of cytochrome c complexes in which the methionine-80 ligand has been replaced by N3-, CN-, or imidazole has been investigated. The N3- and CN-substituted species are reduced by I in a first-order reaction that appears to proceed via a slow dissociation of N3- or CN-, followed by rapid reduction of native cytochrome c. At low concentrations of I, reduction of the imidazole-cytochrome complex occurs by the same mechanism, while, at higher concentrations of I, direct reduction by I and by a monomeric Mo(V) complex in equilibrium with I appears to occur, although at much lower rates than with native cytochrome c. Potentiometric measurements of E degrees for the cytochrome c complexes with N3- and imidazole indicate the lack of reducibility, or reduction in rate relative to native cytochrome c, is not due to thermodynamic reasons. In the case of the CN- complex, E degrees may be too low for direct reduction by I. The effects on the reduction rates are attributed to a conformational change accompanying the replacement of the methionine-80 ligand, which makes the exposed heme edge less available to attack by outer sphere reductants.
mesh_terms: D000818:Animals; D001386:Azides / Q000494:pharmacology; D003486:Cyanides / Q000494:pharmacology; D003545:Cysteine / Q000031:analogs & derivatives; D003574:Cytochrome c Group / Q000378:metabolism*; D004579:Electron Transport; D006736:Horses; D007093:Imidazoles / Q000494:pharmacology; D007700:Kinetics; D008024:Ligands; D008982:Molybdenum / Q000378:metabolism*; D009206:Myocardium; D009942:Organometallic Compounds / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D001386:Azides; D003486:Cyanides; D003574:Cytochrome c Group; D007093:Imidazoles; D008024:Ligands; D009942:Organometallic Compounds; D008982:Molybdenum; D003545:Cysteine