title: The interaction of nitrotyrosine-83 plastocyanin with cytochromes f and c: pH dependence and the effect of an additional negative charge on plastocyanin.
abstract: Spinach plastocyanin was selectively modified using tetranitromethane which incorporates a nitro group ortho to the hydroxyl group of tyrosine 83 (Anderson, G.P., Draheim, J.E. and Gross, E.L. (1985) Biochim. Biophys. Acta 810, 123-131). This tyrosine residue has been postulated to be part of the cytochrome f binding site on plastocyanin. Since the hydroxyl moiety of nitrotyrosine 83 is deprotonated above its pK of 8.3, it provides a useful modification for studying the effect of an extra negative charge on the interaction of plastocyanin with cytochrome f. No effect on cytochrome f oxidation was observed at pH 7 under conditions in which the hydroxyl moiety is protonated. However, the rate of cytochrome f oxidation increased at pH values greater than 8, reaching a maximum at pH 8.6 and decreasing at still higher pH values. The increase was half-maximal at pH 8.3 which is the pK for the hydroxyl moiety on nitrotyrosine 83. In contrast, the rate of cytochrome f oxidation for control plastocyanin was independent of pH from pH 7 to 8.6. These results show that increasing the negative charge on plastocyanin at Tyr-83 increases the ability to react with cytochrome f, supporting the hypothesis that cytochrome f interacts with plastocyanin at this location. In contrast, the reaction of Ntyr-83 plastocyanin with mammalian cytochrome c was independent of pH, suggesting that its mode of interaction with plastocyanin is different from that of cytochrome f. A comparison of the effects of Ntyr-83 modification of plastocyanin with the carboxyl- and amino-group modifications reported previously suggests that plastocyanin binds to cytochrome f in such a way that electrons could be donated to plastocyanin at either of its two binding sites.
authors.affiliation: Department of Biochemistry, Ohio State University, Columbus 43210.
authors.forename: E L
authors.initials: EL
authors.lastname: Gross
authors.forename: A
authors.initials: A
authors.lastname: Curtiss
mesh_terms: D003574:Cytochrome c Group / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism*; D045348:Cytochromes f; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010970:Plastocyanin / Q000378:metabolism*; D011487:Protein Conformation; D014443:Tyrosine / Q000031:analogs & derivatives*
chemical_list: D003574:Cytochrome c Group; D003580:Cytochromes; C002744:3-nitrotyrosine; D014443:Tyrosine; D010970:Plastocyanin; D045348:Cytochromes f