Some redox properties of myohemerythrin from retractor muscle of Themiste zostericola

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Abstract
Distinct semimetmyohemerythrin species are produced by 1-electron oxidation of deoxymyohemerythrin and 1-electron reduction of metmyohemerythrin. The former, (semimetmyo)O, changes (.gtoreq. 90%) to the latter, (semimetmyo)g, with k = 1.0 .times. 10-2 s-1, .**GRAPHIC**. [enthalpy] = 15.1 kcal mol-1, and .**GRAPHIC**. [entropy] = -17 eu. Oxidation of (semimetmyo)O by Fe(CN)63- rapidly produces an unstable metmyohemerythrin form which converts to the final metmyohemerythrin with k = 4.6 .times. 10-3 s-1, .**GRAPHIC**. = 16.8 kcal mol-1, and .**GRAPHIC**. = -13 eu. The 2 met forms react at the same rate with N3-, but the unstable form reacts very rapidly with S2O42- in contrast to stable metmyohemerythrin. (Semimetmyo)R or a mixture of metmyohemerythrin and deoxymyohemerythrin equilibrate very slowly to a mixture containing all 3 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 were used to characterize and measure the rates at 25.degree. C, pH 8.2, and 1 = 0.15 M. The comparative behavior of octameric and monomeric protein is discussed.

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