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Updated: Jun 15, 2026

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method
Published on: July 19, 2019
Coupling and uncoupling mechanisms in the methoxythreonine mutant of cytochrome P450cam: a quantum
Muhannad Altarsha1, Tobias Benighaus, Devesh Kumar
1Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim, Germany.
Abstract:
The Thr252 residue plays a vital role in the catalytic cycle of cytochrome P450cam during the formation of the active species (Compound I) from its precursor (Compound 0). We investigate the effect of replacing Thr252 by methoxythreonine (MeO-Thr) on this protonation reaction (coupling) and on the competing formation of the ferric resting state and H2O2 (uncoupling) by combined quantum mechanical/molecular mechanical (QM/MM) methods. For each reaction, two possible mechanisms are studied, and for each of these the residues Asp251 and Glu366 are considered as proton sources. The computed QM/MM barriers indicate that uncoupling is unfavorable in the case of the Thr252MeO-Thr mutant, whereas there are two energetically feasible proton transfer pathways for coupling. The corresponding rate-limiting barriers for the formation of Compound I are higher in the mutant than in the wild-type enzyme. These findings are consistent with the experimental observations that the Thr252MeO-Thr mutant forms the alcohol product exclusively (via Compound I), but at lower reaction rates compared with the wild-type enzyme.
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