Lm. Geren et al., DESIGN OF A RUTHENIUM CYTOCHROME-C DERIVATIVE TO MEASURE ELECTRON-TRANSFER TO THE INITIAL ACCEPTOR IN CYTOCHROME-C-OXIDASE, The Journal of biological chemistry, 270(6), 1995, pp. 2466-2472
A ruthenium-labeled cytochrome c derivative was prepared to meet two d
esign criteria: the ruthenium group must transfer an electron rapidly
to the heme group, but not alter the interaction with cytochrome c oxi
dase. Site-directed mutagenesis was used to replace His(39) on the bac
kside of yeast C102T iso-1-cytochrome c with a cysteine residue, and t
he single sulfhydryl group was labeled with (4-bromomethyl-4'methylbip
yridine) (bis-bipyridine)ruthenium(II) to form Ru-39-cytochrome c (cyt
c), There is an efficient pathway for electron transfer from the ruth
enium group to the heme group of Ru-39-cyt c comprising 13 covalent bo
nds and one hydrogen bond. Electron transfer from the excited state Ru
(II) to ferric heme c occurred with a rate constant of (6.0 +/- 2.0)
x 10(5) s(-1), followed by electron transfer from ferrous heme c to Ru
(III) with a rate constant of (1.0 +/- 0.2) x 10(6) s(-1), Laser excit
ation of a complex between Ru-39-cyt c and beef cytochrome c oxidase i
n low ionic strength buffer (5 mM phosphate, pH 7) resulted in electro
n transfer from photoreduced heme c to Cu-A with a rate constant of (6
+/- 2) x 10(4) s(-1), followed by electron transfer from Cu-A to heme
a with a rate constant of (1.8 +/- 0.3) x 10(4) s(-1), Increasing the
ionic strength to 100 mM leads to bimolecular kinetics as the complex
is dissociated. The second-order rate constant is (2.5 +/- 0.4) x 10(
7) M(-1) s(-1) at 230 mM ionic strength, nearly the same as that of wi
ld-type iso-1-cytochrome c.