Electron transfer between cytochromes c from horse and Pseudomonas

• Published in: The Journal of biological chemistry 1970-09, Vol.245 (18), p.4653-4657
• Main Authors: Morton, R.A, Overnell, J, Harbury, H.A
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; animal science; Animals; Cytochromes; Electron Transport; Ferricyanides; Horses; Kinetics; Magnetic Resonance Spectroscopy; Osmolar Concentration; Pseudomonas; Spectrophotometry; Temperature; Thermodynamics; zoology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)62844-3

The rate of electron transfer between horse cytochrome c and Pseudomonas cytochrome c 551 has been examined by stopped flow spectrophotometry. Experiments were conducted at temperatures from 4.5 to 32.5° and ionic strengths from 0.03 to 0.32. The pH was maintained at 7.0 with 0.02 m potassium phosphate buffer. Comparative data were obtained for the reaction of cytochrome c with potassium ferricyanide under these conditions. Whereas the rate of the ferricyanide reaction varied with the ionic strength, but not the temperature, the reverse held true for the reaction between cytochrome c and cytochrome c 551. The latter process was insensitive to changes in the ionic strength, and exhibited an activation energy of 12 kcal per mole. The equilibrium constant was found to be 1 at all temperatures. At 4.5°, pH 7.0, and an ionic strength of 0.2, a second order rate constant of 1.57 ± 0.18 x 10 4 m -1 sec -1 was obtained. Although Pseudomonas cytochrome c 551 and horse cytochrome c differ markedly in primary structure, and are oppositely charged at neutral pH, the rate of electron transfer at 20° corresponds closely to that previously estimated from nuclear magnetic resonance data for the electron exchange reaction between horse ferri- and ferrocytochrome c at this temperature.