Manganese-Substituted Myoglobin: Characterization and Reactivity of an Oxidizing Intermediate towards a Weak C-H Bond

Metal-substituted hemoproteins have been examined by biochemists for decades, but their potential for diverse functionalities has not been thoroughly investigated. By replacing hemoproteins with non-native metals, heme-containing proteins could be capable of performing a range of chemistries not allowed for in the native protein. The metal within the heme of the oxygen-carrying hemoprotein, myoglobin, can readily be replaced with other first row transition metals such as cobalt, chromium and manganese. Upon oxidation with two-electron oxidants (ex. meta-chloroperbenzoic acid), an oxidizing intermediate is produced in manganese-substituted myoglobin. Electron paramagnetic resonance analyses confirm the oxidation of Mn(III) to Mn(IV). With the addition of weak C-H bonds of 1,4 cyclohexadiene, hydrogen atom abstraction is exhibited by the oxidizing intermediate that displays a second-order rate constant of 2.79 +/- 0.22 M-1 s(-1) by the metal-oxo species. The replacement of the iron ion with a manganese ion at the active site of myoglobin displays oxidative capabilities that are not shown in native myoglobin.