Craig Fenwick, Stephen Marmor, K. Govindaraju, Ann M. English, James F. Wishart and Ji Sun
J. Am. Chem. Soc. 116, 3169-3170 (1994)
Abstract:
The observed rate constant (kobs), as determined by pulse radiolysis, for intramolecular electron transfer (ET) from a5RuII bound at His48 to the ferric heme of horse heart myoglobin was 0.059 ± 0.003 s-1 at 25 °C, pH 7.0. This value is essentially identical to that previously reported in the literature for sperm whale myoglobin. Following oxidation by H2O2 of the ferric heme to oxyferryl heme (FeIV=O), kobs for intramolecular ET from a5RuII(His48) to heme increased to 0.19 ± 0.02 s-1 at a driving force of 0.96 eV. However, at the same driving force, a rate constant of 105 s-1 has been reported for intramolecular ET to the Zn porphyrin cation in the a5Ru(His48) derivative of Zn-substituted myoglobin. The ~106-fold slower rate of reduction of the FeIV=O heme compared to the Zn porphyrin cation suggests different rate-determing steps for intramolecular ET in the two myoglobin derivatives.