Electron-transfer self-exchange kinetics of trimethylphosphine horse-heart myoglobin

Electron self-exchange has been measured by an NMR technique for horse-heart myoglobin. The rate is 3.1 x 10(3) M-1 s-1 at 23 degrees in 0.1 M phosphate at pH 6.9. The rate was weakly dependent on ionic strength up to 0.7 M in added KCl (3.9 x 10(3) M-1 s-1). The enthalpy of activation was 12.1 +/- 0.5 kcal mol-1, and the entropy of activation was -1.2 +/- 0.5 cal mol-1 deg-1. Analysis of the data in terms of the Marcus theory gives a reorganization energy, lambda, for self-exchange of 1.6 eV mol-1.