Zhang J, Hoogmartens J, Van Schepdael A. Kinetic study of cytochrome P450 by capillary electrophoretically mediated microanalysis.
Electrophoresis 2008;
29:3694-700. [PMID:
18803184 DOI:
10.1002/elps.200700942]
[Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
An electrophoretically mediated microanalysis method for the determination of CYP3A4 activity using testosterone and nifedipine as substrates was developed. Initially, the enzymatic reaction was performed off-line and the samples were subsequently injected into the capillary by pressure. The CYP3A4 activity was determined by quantitation of the reactant cofactor, NADPH. To further optimize, speed-up and miniaturize the enzyme assay, the enzymatic reaction was performed directly in the capillary, prior to separation and quantitation of the product cofactor, NADP, employing the plug-plug mode of electrophoretically mediated microanalysis. An amplification step was introduced by means of an on-capillary incubation of 15 min, in order to accumulate enough reaction product to detect spectrophotometrically at 260 nm. This setup resulted in a fully automated assay, which can be carried out in less than 35 min. Using the Lineweaver-Burk equation, the Michaelis constants (K(m)) for the oxidation of testosterone and nifedipine by CYP3A4 were calculated to be 58.6+/-8.3 and 19.1+/-2.4 microM, respectively, which are consistent with off-line assay and previously reported values.
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