Heterogeneity of the coumarin anticoagulant targeted vitamin K epoxide reduction system. Study of kinetic parameters in susceptible and resistant mice (Mus musculus domesticus).
Vitamin K epoxide reductase (VKOR) activity in liver microsomes from a susceptible and a genetically warfarin-resistant strain of mice (Mus Musculus domesticus) was analyzed to determine the mechanism of resistance to this 4-hydroxycoumarin derivative. Kinetic parameters for VKOR were calculated for each strain by incubating liver microsomes with vitamin K epoxide +/- warfarin. In susceptible mice, an Eadie-Hofstee plot of the data was not linear and suggested the involvement of at least two different components. Apparent kinetic parameters were obtained by nonlinear regression using a Michaelis--Menten model, which takes into account two enzymatic components. Component A presents a high K(m) and a high V(m), and as a consequence only an enzymatic efficiency V(m)/K(m) was obtained (0.0024 mL/min/mg). Estimated warfarin K(i) was 0.17 muM. Component B presented an apparent K(m) of 12.73 muM, an apparent V(m) of 0.32 nmol/min/mg, and an apparent K(i) for warfarin of 6.0 muM. In resistant mice, the enzymatic efficiency corresponding to component A was highly decreased (0.0003-0.00066 mL/min/mg) while the K(i) for warfarin was not modified. The apparent V(m) of component B was poorly modified between susceptible and resistant mice. The apparent K(m) of component B observed in resistant mice was similar to the K(m) observed in susceptible mice. These modifications of the catalytic properties are associated with a single nucleotide polymorphism (T175G) in the VKOR-C1 gene, which corresponds to a Trp59Gly mutation in the protein. (c) 2006 Wiley Periodicals, Inc. J Biochem Mol Toxicol 20:221-229, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20144.[1]References
- Heterogeneity of the coumarin anticoagulant targeted vitamin K epoxide reduction system. Study of kinetic parameters in susceptible and resistant mice (Mus musculus domesticus). Lasseur, R., Grandemange, A., Longin-Sauvageon, C., Berny, P., Benoit, E. J. Biochem. Mol. Toxicol. (2006) [Pubmed]
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