Intracomplex electron transfer between ruthenium-cytochrome c derivatives and cytochrome c oxidase.
The reactions of bovine cytochrome c oxidase with horse cytochrome c derivatives labeled at specific lysine amino groups with (dicarboxybipyridine)bis(bipyridine)ruthenium (II) were studied by laser flash photolysis. All of the derivatives form complexes with cytochrome c oxidase at low ionic strength (5 mM sodium phosphate, pH 7). Excitation of Ru(II) to Ru(II*) with a short laser flash resulted in rapid electron transfer to the ferric heme group of cytochrome c, followed by electron transfer to cytochrome c oxidase. The photoreduced heme Fe(II) in the cytochrome c derivative modified at lysine 25 on the periphery of the heme crevice domain transferred an electron to CuA with a rate constant of 1.1 x 10(4) s-1. CuA then transferred an electron to cytochrome a with a rate constant of 2.3 x 10(4) s-1. The derivatives modified at lysines 7, 39, 55, and 60 remote from the heme crevice domain of cytochrome c have nearly the same kinetics. The rate constant for electron transfer from the cytochrome c heme to CuA is greater than 10(5) s-1, and the rate constant for electron transfer from CuA to cytochrome a is 2 x 10(4) s-1. The cytochrome c derivatives modified at lysines 13 and 27 in the heme crevice domain react much more slowly than the other derivatives, with intracomplex rate constants for oxidation of cytochrome c ranging from 1000 to 6000 s-1. The bulky ruthenium group at the heme crevice domain of these derivatives apparently alters the binding orientation, leading to smaller electron-transfer rates.(ABSTRACT TRUNCATED AT 250 WORDS)
Pan
L P
LP
Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville 72701.
Hibdon
S
S
Liu
R Q
RQ
Durham
B
B
Millett
F
F
D000818:Animals; D002417:Cattle; D003574:Cytochrome c Group / Q000378:metabolism*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006736:Horses; D007700:Kinetics; D010782:Photolysis; D012428:Ruthenium / Q000378:metabolism*; D013816:Thermodynamics; D013997:Time Factors
D003574:Cytochrome c Group; D012428:Ruthenium; D003576:Electron Transport Complex IV