Mephenytoin metabolism in vitro by human liver.
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.
Jurima
M
M
Inaba
T
T
Kalow
W
W
D006801:Humans; D006827:Hydantoins / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008617:Mephenytoin / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000378:metabolism
D006827:Hydantoins; D006899:Mixed Function Oxygenases; D008617:Mephenytoin