title: Cytochrome P450CAM enzymatic catalysis cycle: a quantum mechanics/molecular mechanics study.
abstract: The catalytic pathway of cytochrome P450cam is studied by means of a hybrid quantum mechanics/molecular mechanics method. Our results reveal an active role of the enzyme in the different catalytic steps. The protein initially controls the energy gap between the high- and low-spin states in the substrate binding process, allowing thermodynamic reduction by putidaredoxin reductase and molecular oxygen addition. A second electron reduction activates the delivery of protons to the active site through a selective interaction of Thr252 and the distal oxygen causing the O--O cleavage. Finally, the protein environment catalyzes the substrate hydrogen atom abstraction step with a remarkably low free energy barrier ( approximately 8 kcal/mol). Our results are consistent with the effect of mutations on the enzymatic efficacy and provide a satisfactory explanation for the experimental failure to trap the proposed catalytically competent species, a ferryl Fe(IV) heme.
authors.affiliation: Department of Chemistry and Center for Biomolecular Simulations, Columbia University, New York, New York 10027, USA.
authors.forename: Victor
authors.initials: V
authors.lastname: Guallar
authors.forename: Richard A
authors.initials: RA
authors.lastname: Friesner
mesh_terms: D002164:Camphor / Q000737:chemistry / Q000378:metabolism; D019475:Camphor 5-Monooxygenase / Q000737:chemistry* / Q000378:metabolism*; D002384:Catalysis; D005290:Ferric Compounds / Q000737:chemistry; D006900:Hydroxylation; D008958:Models, Molecular; D011789:Quantum Theory; D013481:Superoxides / Q000737:chemistry
chemical_list: D005290:Ferric Compounds; D013481:Superoxides; C000499:ferric oxide; D002164:Camphor; D019475:Camphor 5-Monooxygenase