Protoheme reactivity

Peroxidases (EC 1.11.1.7), which have ferric protoheme prosthetic groups, react non-selectively via free radical mechanisms, using hydrogen peroxide as the electron acceptor. A reactive Fe(IV)-0 species and a radical heme intermediate are formed, and the intermediate then reacts with the reducing substrate to produce the oxidized product, regenerating the Fe(III) ion. 

Petrich, J. W. Poyart, C. Martin, J. L., Photophysics and reactivity of heme proteins A femtosecond absorption study of hemoglobin, myoglobin, and protoheme. Biochemistry 1988, 27, 4049 060. 

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