The effect of complex-formation with polyanions on the redox properties of cytochrome c.
1. The stable complex formed between mammalian cytochrome c and phosvitin at low ionic strength was studied by partition in an aqueous two-phase system. Oxidized cytochrome c binds to phosvitin with a higher affinity than reduced cytochrome c. The difference was equivalent to a decrease of the redox potential by 22 mV on binding. 2. Complex-formation with phosvitin strongly inhibited the reaction of cytochrome c with reagents that react as negatively charged species, such as ascorbate, dithionite, ferricyanide and tetrachlorobenzoquinol. Reaction with uncharged reagents such as NNN'N'-tetramethylphenylenediamine and the reduced form of the N-methylphenazonium ion (present as the methylsulphate) was little affected by complex-formation, whereas oxidation of the reduced cytochrome by the positively charged tris-(phenanthroline)cobalt(III) ion was greatly stimulated. 3. A similar pattern of inhibition and stimulation of reaction rates was observed when phosvitin was replaced by other macromolecular polyanions such as dextran sulphate and heparin, indicating that the results were a general property of complex-formation with polyanions. A weaker but qualitatively similar effect was observed on addition of inositol hexaphosphate and ATP. 4. It is suggested that the effects of complex-formation with polyanions on the reactivity of cytochrome c with redox reagents are mainly the result of replacing the positive charge on the free cytochrome by a net negative charge. Any steric effects on polyanion binding are small in comparison with such electrostatic effects.
D000838:Anions; D001205:Ascorbic Acid; D055598:Chemical Phenomena; D002621:Chemistry; D003574:Cytochrome c Group; D003911:Dextrans; D004527:Egg Proteins; D046911:Macromolecular Substances; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D010774:Phosvitin; D011092:Polyethylene Glycols
D000838:Anions; D003574:Cytochrome c Group; D003911:Dextrans; D004527:Egg Proteins; D046911:Macromolecular Substances; D011092:Polyethylene Glycols; D010774:Phosvitin; D001205:Ascorbic Acid