Ji Sun and James F. Wishart
Inorg. Chem. 37, 1124-1126 (1998) [Find paper at ACS Publications] or use ACS Articles on Request
Abstract:
Manganese-substituted horse heart cytochrome c was prepared by replacing the iron in the heme group according to established methods. The resulting manganicytochrome c was subsequently modified at histidine-33 with three ruthenium complexes trans-(NH3)4(L)Ru-His33, where L = NH3, pyridine or isonicotinamide. Proof of correct derivatization was obtained by atomic absorption analysis of manganese and ruthenium, differential pulse voltammetry and electrospray mass spectroscopy. Manganese(II)-to-ruthenium(III) intramolecular electron transfer rates were measured as a function of temperature by pulse radiolysis, using oxidation by azide radical (N3*) to generate the desired electron transfer precursors from the fully reduced forms. The observed intramolecular electron transfer rates at 25 C are: NH3, 41 s-1; pyridine, 446 s-1; and isonicotinamide, 667 s-1; for a driving forces of -0.08, -0.31, and -0.38 eV, respectively. The corresponding intermolecular electron transfer rates (from one MnIICyt c to a ruthenium(III) bound to another MnCyt c) are 5 x 105, 9.9 x 106, and 2.7 x 107 M-1 s-1. The results are compared with analogous ruthenium-modified, native iron and cobalt-substituted cytochromes c.