Mechanism-based inactivation of human cytochrome P450 1A2 by furafylline: detection of a 1:1 adduct to protein and evidence for the formation of a novel imidazomethide intermediate.
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Racha JK, Rettie AE, Kunze KL
Mechanism-based inactivation of human cytochrome P450 1A2 by furafylline: detection of a 1:1 adduct to protein and evidence for the formation of a novel imidazomethide intermediate.
Biochemistry. 1998 May 19;37(20):7407-19. doi: 10.1021/bi973011m.
- PubMed ID
- 9585555 [ View in PubMed]
- Abstract
The rapid loss of human CYP1A2 (cytochrome P450 1A2) activity caused by the 8-methylxanthine furafylline is investigated with the aim of determining whether a stable covalent adduct of the xanthine to the enzyme could be identified. Metabolic studies employing expressed CYP1A2 with radiolabeled furafylline and a close analogue, cyclohexylline, where the furan ring is replaced with cyclohexane, indicate that these xanthines are bound in a 1:1 ratio to CYP1A2 protein. This result, combined with earlier kinetic studies, verifies that these compounds are mechanism-based inhibitors of the enzyme. The 8'-methyl carbinols are the only metabolites formed by CYP1A2, and substantial (70-80%) incorporation of oxygen from the medium into the carbinols is observed. Carbinol formation is further characterized by high intramolecular isotope effects (kH/kD > 9) and low intermolecular isotope effects (DV/K < 2). Overall partition ratios are low (5.0 and 7.6, respectively), confirming our previous conclusion that furafylline is an efficient inactivator. By contrast, the N7-methyl-8-methylxanthines are good substrates for CYP1A2 but are not themselves inactivating agents. In addition to other metabolic products, the 8'-methyl carbinols of these N7-methyl-8-methylxanthines are formed in substantial amounts with equally high intramolecular isotope effects; however, the carbinol oxygen is derived exclusively from molecular oxygen. We conclude that oxidation of the 8-methyl group of furafylline and cyclohexylline, but not their N7-methyl analogues, by CYP1A2 promotes a major fraction of the inactivating xanthines to a two electron oxidized intermediate which either terminates enzyme activity by reaction with an active site amino acid or is decomposed by reaction with the medium to give carbinol.
DrugBank Data that Cites this Article
- Drug Enzymes
Drug Enzyme Kind Organism Pharmacological Action Actions Furafylline Cytochrome P450 1A2 Protein Humans NoInhibitorDetails