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

Abstract

Rate constants for the reactions of horse cytochrome c (E'0 of +260 mV) with the copper proteins Anabaena variabilis plastocyanin (E'0 of +360 mV) used as oxidant and stellacyanin (E'0 of +187 mV) used as reductant have been determined at 25 degrees C, pH 7.5 and 7.0, respectively, and an ionic strength of 0.10 M (NaCl). These rate constants were also measured with eight different singly substituted 4-carboxy-2,6-dinitrophenyl (CDNP) horse cytochrome c derivatives, modified at lysine-7, -13, -25, -27, -60, -72, -86, or -87 and with the trinitrophenyl (TNP) derivative modified at lysine-13. The influence of the modifications on the bimolecular rate constants for these reactions defines the region on the protein that is involved in the electron-exchange reactions and demonstrates that the preferred site is at or near the solvent-accessible edge of the heme prosthetic group on the "front" surface of the molecule. Both reactions are strongly influenced by the lysine-72 modification to the left of the exposed heme edge and, to this extent, behave similar to the earlier studied reaction with azurin. These effects span only an order of magnitude in rate constants and are thus many times smaller than those for the physiological protein redox partners of cytochrome c. While the preferred sites of reaction on the surface of cytochrome c for small inorganic complexes appear to be dependent only on the net charge of the reactants, with the copper proteins additional factors intervene. These influences are discussed in terms of hydrophobic patches and the distribution of charges on the surface of the four copper proteins so far examined.

Electron-transfer reactions of cytochrome f with flavin semiquinones and with plastocyanin. Importance of protein-protein electrostatic interactions and of donor-acceptor coupling

“…Previous Studies. Although cytochrome c is not a physiological partner of plastocyanin, their reaction has been studied (Armstrong et al, 1986;Augustin et al, 1983;Bagby et al, 1990a,b;Chapman et al, 1984;King et al, 1985;Pan et al, 1990;Peerey & Kostic, 1989;Roberts et al, 1991; Senthilathipan & Zhou & Kostic, 1991a,b, 1992 as much as the reaction between the true partners cytochrome/and plastocyanin (Anderson et al, 1987;Beoku-Betts et al, 1983Morand et al, 1989;Niwa et al, 1980;Takabe et al, 1980Takabe et al, , 1984Takabe et al, , 1989Tanaka et al, 1981;Takenaka et al, 1980;Takabe & Ishikawa, 1989; Wherland & Pecht, 1978;Wood, 1974). Unavoidable autoreduction (Garewal et al, 1974;Garewal & Wasserman, 1972;Tanaka et al, 1978) and aggregation (Gray, 1978) complicate work with cytochrome /.…”

Photoinduced electron-transfer reaction in a ternary system involving zinc cytochrome c and plastocyanin. Interplay of monopolar and dipolar electrostatic interactions between metalloproteins

“…In the absence of cupriplastocyanin; (b) in the presence of 30 µ cupriplastocyanin. around the exposed heme edge abuts the broad negatively charged patch remote from the copper atom (Augustin et al, 1983;Armstrong et al, 1986;Anderson et al, 1987;Burkey & Gross, 1981Chapman et al, 1984;Geren et al, 1983;King et al, 1985;Bagby et al, 1990;Roberts et al, 1991). Much evidence shows that direct amide cross-links between lysine residues in cytochrome c and acidic residues in plastocyanin reinforce this very orientation (Geren et and Kostió (1991a).'…”

Importance of protein rearrangement in the electron-transfer reaction between the physiological partners cytochrome f and plastocyanin

“…Because of these difficulties and because three-dimensional structures of cytochrome c in the crystalline state and in solution, in both ferric and ferrous oxidation states, are known (Berghuis & Brayer, 1992;Bushnell et al, 1990;Gao et al, 1989), electron-transfer reactions of plastocyanin with this protein and its derivatives have been studied (Armstrong et al, 1986;Augustin etal., 1983 ;Bagby etal., 1990a,b;Brothers etal., 1993;Chapman etal., 1984; de Silva etal., 1992;Gross & Curtiss, 1991; King etal., 1985;Kostió, 1991, and references therein;Modi et al, 1992a;Pan et al, 1990;Peerey & Kostió, 1989;Roberts et al, 1991; Senthilathipan & Tollin, 1989;Takenaka & Takabe, 1984; Zhou & Kostió, 1991a,b, 1992aZhou et al, 1992) as much as its reaction with the true physiological partner, cytochrome f. Electron-transfer re-actions between cytochrome c and plastocyanin are interesting in their own right, but caution is necessary if cytochrome c is considered a model or a replacement for cytochrome f.…”