Abstract
Human liver was used in investigations of mephenytoin p-hydroxylase, the enzyme presumably responsible for the genetic polymorphism in mephenytoin metabolism. A gas chromatographic assay method was developed to measure p-hydroxylation and N-demethylation which is the other major metabolic pathway. Both reactions were localized in the microsomal fraction and required NADPH. Inhibition of p-hydroxylation by CO, SKF 525-A, and metyrapone was demonstrated. It was concluded that a form of cytochrome P-450 catalyzes the reaction. The velocity of N-demethylation in human liver did not show saturation even at 500 microM substrate concentration. The p-hydroxylation, however, followed Michaelis-Menten kinetics. The Km, determined in five different livers, ranged from 59 to 143 microM. The linearity in Eadie-Hofstee plots was consistent with the involvement of a single catalytic site.
DMD articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|
