title: A proficient enzyme revisited: the predicted mechanism for orotidine monophosphate decarboxylase.
abstract: A mechanism is proposed to explain the activity of orotidine 5'-monophosphate decarboxylase (ODCase). This enzyme is the one of the most proficient known, with a catalytic proficiency (kcat/Km)/knon = 10(23) M-1. Quantum mechanical calculations predict a mechanism involving a stabilized carbene intermediate, which represents a previously unrecognized mode of enzymatic activity for ODCase. The proposed mechanism involves proton transfer from a weak acid (pKa = 7, where Ka is the acid constant) concerted with decarboxylation, in a nonpolar enzyme environment. Such a mechanism makes possible different approaches to the design of ODCase inhibitors. Furthermore, the prediction that general acid catalysis may only be effective in low dielectric media is of general significance for understanding the activity of many enzymes.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA.
authors.forename: J K
authors.initials: JK
authors.lastname: Lee
authors.forename: K N
authors.initials: KN
authors.lastname: Houk
mesh_terms: D001463:Barbiturates / Q000494:pharmacology; D001665:Binding Sites; D002384:Catalysis; D003653:Decarboxylation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009964:Orotidine-5'-Phosphate Decarboxylase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011522:Protons; D013816:Thermodynamics; D014542:Uridine Monophosphate / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D001463:Barbiturates; D004791:Enzyme Inhibitors; D011522:Protons; C005417:orotidylic acid; D014542:Uridine Monophosphate; D009964:Orotidine-5'-Phosphate Decarboxylase