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

Abstract

Reduction of turnip ferricytochrome f by flavin semiquinones and oxidation of this ferrocytochrome f by French bean cupriplastocyanin are studied by laser flash photolysis over a wide range of ionic strengths. Second-order rate constants (+/- 15%) at extreme values of ionic strength, all at pH 7.0 and 22 degrees C, are as follows: with FMN semiquinone at 1.00 and 0.0040 M, 5.0 x 10(7) and 3.9 x 10(8) M-1 s-1; with riboflavin semiquinone at 1.00 and 0.0040 m, 1.7 x 10(8) and 1.9 x 10(8) M-1 s-1; with lumiflavin semiquinone at 1.00 and 0.0045 M, 1.8 x 10(8) and 4.5 x 10(8) M-1 s-1; with cupriplastocyanin at 1.00 and 0.100 M, 1.4 x 10(6) and 2.0 x 10(8) M-1 s-1. These reactions of cytochrome f are governed by the local positive charge of the interaction domain (the exposed heme edge), not by the overall negative charge of the protein. Lumiflavin semiquinone behaves as if it carried a small negative charge, probably because partial localization of the odd electron gives this electroneutral molecule some polarity; local charge seems to be more important than overall charge even for relatively small redox agents. The dependence of the rate constants on ionic strength was fitted to the equation of Watkins; this model recognizes the importance of local charges of the domains through which redox partners interact. There is kinetic evidence that a noncovalent complex between cytochrome f and plastocyanin exists at low ionic strength.(ABSTRACT TRUNCATED AT 250 WORDS)

The Structure and Unusual pH Dependence of Plastocyanin from the Fern Dryopteris crassirhizoma

“…From these reaction studies and comparative investigations using the acidic patch mutants, it has been suggested that a physiological electron donor, cytochrome f, might interact with the acidic patch of plastocyanin. Qin and Kostic (19,20) have suggested that the rearrangement of the electron transfer site between * This work was supported by Grants-in-Aid for Science Research on Priority Areas from the Ministry of Education, Science, Sports and Culture, Japan, by the Joint Studies of Program (1997) of the Institute for Molecular Science, and by the Grant-in-Aid for the Ground Experiment for the Space Utilization from the Japan Space Forum and National Space Developments Agency of Japan to Kohzuma. The costs of publication of this article were defrayed in part by the payment of page charges.…”

Electron Transfer from the Rieske Iron-Sulfur Protein (ISP) to Cytochrome f in Vitro

“…Typical traces of the kinetics of cytochrome f reduction at pH 5.6 and 7.5 are shown in Fig 3A and summarized in Table I. Under the same reaction conditions, the rate of electron transfer from cytochrome f to PC is more rapid, with k 2 (f-PC) ϳ 200 ϫ 10 6 and 50 ϫ 10 6 M Ϫ1 s Ϫ1 , respectively, at pH 7, and 0.01 and 0.2 M ionic strength (6,32). No variation in the k 2 (ISP-f) was observed between ionic strengths of 0.01 and 0.10 M, nor between pH 7.5 and 5.6.…”

Interaction of plastocyanin with oligopeptides: effect of lysine distribution within the peptide

“…It has been shown that the Cu-remote negative patch of PC and the positively charged site of cyt f interact through electrostatic interactions to form a PC-cyt f complex for electron transfer [11][12][13][14][15][16][17][18][19][20][21]. The hydrophobic patch of PC, however, has also been shown to be crucial for the PC-cyt f complex [22,25,26].…”