The heme-thiolate peroxygenase of Agrocybe aegerita is a remarkably capable biocatalyst and a mechanistic analog of cytochrome P450. The stability of this fungal protein has provided a rare opportunity to study P450-like C−H hydroxylation in a novel and unrelated enzyme. Both APO-I and APO-II have been generated, and their redox potentials have been determined. The ferryl species Cys−S−Fe^IV−OH (APO-II) has been generated cleanly via reduction of the corresponding APO-I and a basic pK_a revealed for the Cys−S−Fe^IV−OH ⇄ Cys−S−Fe^IV=O equilibrium. Most significantly, APO-II displays surprisingly high reactivity toward benzylic C−H (bond-dissociation energy 80−86 kcal/mol) and phenolic substrates with rate constants orders of magnitude larger than those of typical peroxidases or model compounds due to the basic ferryl.

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