Some redox properties of myohemerythrin from retractor muscle of Themiste zostericola.

Distinct semimetmyohemerythrin species are produced by one-electron oxidation of deoxymyohemerythrin and one-electron reduction of metmyohemerythrin. The former, (semimetmyo)o, changes (greater than or equal to 90%) to the latter, (semimetmyo)R, with k = 1.0 x 10(-2) s-1, delta H = 15.1 kcal mol-1 and delta S = -17 eu. Oxidation of (semimetmyo)o by Fe(CN)6(3)- rapidly produces an unstable metmyohemerythrin form which converts to the final metmyohemerythrin with k = 4.6 x 10(-3) s-1, delta H = 16.8 kcal mol-1, and delta S = -13 eu. The two met forms react at the same rate with N3-, but the unstable form reacts very rapidly with S2O4(2-) in contrast to stable metmyohemerythrin. (Semimetmyo)R or a mixture of metmyohemerythrin and deoxymyohemerythrin equilibrate very slowly to a mixture containing all three species. The rate constants for disproportionation and comproportionation are 0.89 M-1 s-1 and 9.4 M-1 s-1, respectively. EPR spectra near liquid He temperatures and optical absorption spectra have been used to characterize and measure the rates at 25 degrees C, pH 8.2, and I = 0.15 M. The comparative behavior of octameric and monomeric protein is discussed.