Preferred sites for electron exchange between cytochrome c and [Fe(edta)]2? and [Co(sep)]2+ complexes

Abstract

Rate constants (25 "C) for the reduction of eight different singly substituted 4-carboxy-2,6dinitrophenyl (cdnp) horse heart cytochrome c derivatives, modified respectively at lysine 7, 13,25,27,60,72,86, and 87, and of one 2,4,6-trinitrophenyl (tnp) derivative modified at lysine 13, by the 2-and 2 + complexes [Fe(edta)l2-(edta = ethylenediaminetetra-acetate) and [Co(sep)]'+ (sep =

Preferred sites on cytochrome c for electron transfer with two positively charged blue copper proteins, Anabaena variabilis plastocyanin and stellacyanin

“…Interestingly, in similar studies of the modified cytochrome c derivatives with inorganic complexes, it was found that the negatively charged [Fe(CN)6]3" is most influenced by lysine-72 to the left of the exposed heme edge, whereas positively charged [Co(phen)3]3+ is most influenced by lysine-27 to the right of the exposed heme edge, on the front surface of the molecule (Butler et al, 1983). Studies with [Fe(EDTA)]2and the sepulchrate cage complex [Co(sep)]2', as reductants for cytochrome c(III), are in agreement with this picture and reinforce it as well (Armstrong et al, 1986). Thus, it is possible that the region on the surface of cytochrome c capable of accepting or donating an electron is not very limited and extends to both sides of the exposed heme edge.…”

“…The negatively charged small inorganic reactants would tend to impact at the most positively charged part of that area, while the positively charged small reactants would tend to approach the least positively charged area still capable of electron exchange. Such a situation would explain the earlier observations (Butler et al, 1983; Armstrong et al, 1986).…”

Bimolecular Electron Transfer in the Marcus Inverted Region

“…The distance dependence of V is exponential and given by 86 where d is the edge-to-edge distance between the Ru II diimine and the heme of the protein and acceptor and V (0) is the value of V at d = d 0 , which has been defined to be 3 Å to account for the electron clouds about the outermost atoms of each reactant. 47a, For cyt c , β is 1.2 Å -1 and V (0) is 200 cm -1 . 47a,, It is well established that the ET reactions of cationic metal complexes featuring hydrophobic ligation spheres proceed at the exposed heme edge of the protein. , Singly modified peptide and NMR studies show that positively charged reactants access the recessed heme edge near Lys-27, ,, thereby permitting us to relate the edge-to-edge ET distance, d , in eq 10, to the protein and Ru II diimine center-to-center distance, r . The distance from the outermost meso position of the heme to the center of the protein, determined from the crystal structure of cyt c , corresponds to 9.1 Å .…”

Electron-transfer‐mediated binding of optically active cobalt(III) complexes to horse heart cytochromec

“…cytochrome c1, cytochrome oxidase and cytochrome peroxidase), as well as with low molecular weight metal complexes. For the binding of the latter in the precursor complex, NMR and kinetic measurements, as a function of ionic strength and chemical modifications of the surface residues of the protein, have allowed researchers to determine three generally reactive areas (Brautigan et al 1978;König et al 1980;Webb et al 1980;Ahmed & Millett 1981;Butler et al 1981Butler et al , 1983Boswell et al 1982;Eley et al 1982;Koppenol & Margoliash 1982;Williams et al 1982;Moore et al 1984;Armstrong et al 1986;Drake et al 1989). These areas, located on both sides of the haem, are found to react preferentially either with anionic or cationic species.…”