ISSN:
1432-1912
Keywords:
Methylphenobarbital
;
Liver Microsomes
;
Cytochrome P-450
;
Stereoselectivity
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary N-Demethylation to phenobarbital is the only detectable monooxygenation pathway for (+)- and (−)-methylphenobarbital in rat liver microsomes. In microsomes from control ratsV max is about 3.5-fold higher for the (+)-isomer than for the (−)-form. This ratio increases significantly to 5 after pretreatment of rats with phenobarbital. Qualitatively similar but smaller ratios are found for the magnitude of the substrate binding spectra with corresponding values of 1.7 for control and 2.5 for phenobarbital treated rats. The spectral dissociation constants (K s) and the distribution of both enantiomers between water and the microsomal membranes are not significantly different. Since only cytochrome P-450 is involved in the N-demethylation of both enantiomers the participation of two phenobarbital-inducible species of cytochrome P-450 with different Stereoselectivity is suggested. This is proved by inhibition studies with metyrapone which forms complexes more easily with the species responsible for the preferential binding and N-demethylation of the (+)-isomer of methyl phenobarbital.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00997298
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