Electron transfer to ferricytochrome c: reaction with hydrated electrons and conformational transitions involved.
The reaction of horse-heart cytochrome c with hydrated electrons has been studied by the pulseradiolysis technique. In neutral solution, the ferriheme group was reduced in a bimolecular reaction that takes place at a rate equal to that of the decay of the e(-) (aq), and approaches the diffusion-controlled limit. This reduction is assigned mainly to a direct reaction, proceeding via the exposed edge of the porphyrin projecting into the cytochrome c crevice. The reaction absorption spectrum observed 20 musec after an electron pulse was very similar, yet blue-shifted relative to, the difference spectrum between the reduced and oxidized forms of cytochrome c. However, this shift vanishes in a slow monomolecular reaction, which seems to reflect the conformational relaxation of the protein to the final equilibrium state of its reduced form. In alkaline solutions, the transition of cytochrome c molecules into an irreducible conformation causes a proportionate decrease in the amount of ferricytochrome c reduced in the direct reaction. The rate of conformational transition of the protein into the reactive form is now the limiting step for a substantial part of the reduction that takes place via this slow monomolecular reaction. Pseudomonas cytochrome c 551 which, in contrast to horse-heart cytochrome c, is a negatively charged protein at neutral pH reacts with e(-) (aq) at a rate lower than does the horse-heart protein. The reduction of the heme group follows that of the e(-) (aq) decay with a small, yet significant, delay.
D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D003580:Cytochromes / Q000528:radiation effects; D004579:Electron Transport; D006736:Horses; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008722:Methods; D009206:Myocardium / Q000201:enzymology; D010084:Oxidation-Reduction; D011487:Protein Conformation; D011551:Pseudomonas fluorescens / Q000201:enzymology; D011674:Pulse; D011830:Radiation Effects; D013057:Spectrum Analysis; D014466:Ultraviolet Rays
D003580:Cytochromes