Significant electron transfer in heme catalysis: The case of chlorite dismutase

Abstract

Electron transfer (ET) is significant in heme catalysis but usually difficult to be characterized. In the present DFT calculations, a transition state for ET has been optimized during the decomposition of peracetic acid (PAA) catalyzed by chlorite dismutase (Cld), using an active-site model based on the X-ray crystal structure of Cld. The Cld-catalyzed PAA reaction is revealed to proceed via a homolytic OO bond cleavage to transiently form compound II (Cpd II) and acetate radical (OAc), and a subsequent fast ET from Cpd II porphyrin to OAc leading to compound I (Cpd I) and acetate anion. The second step of ET is rate-limiting. The results highlight the importance of ET in heme chemistry and imply that the mechanisms of heme enzymes may be masked by fast ET even if a key intermediate has been detected (like Cpd I in this case). The comparison with the Cld-catalyzed chlorite reaction further indicates that a heme enzyme may employ different mechanisms for different substrates.