PT  - JOURNAL ARTICLE
AU  - D. S. SITAR
AU  - G. J. MANNERING
TI  - DETERMINATION OF APPARENT KINETIC CONSTANTS OF THE MICROSOMAL HYDROXYLATION OF AMOBARBITAL, HEXOBARBITAL, AND PENTOBARBITAL
DP  - 1973 Sep 01
TA  - Drug Metabolism and Disposition
PG  - 663--668
VI  - 1
IP  - 5
4099  - http://dmd.aspetjournals.org/content/1/5/663.short
4100  - http://dmd.aspetjournals.org/content/1/5/663.full
SO  - Drug Metab Dispos1973 Sep 01; 1
AB  - Apparent kinetic constants for the hydroxylation of amobarbital, hexobarbital, and pentobarbital by hepatic microsomes from the rat were obtained by measuring product formation as determined by high-pressure anion exchange chromatography. Michaelis constants (millimolar) and maximum velocities (nanomoles of product formed per nmol of cytochrome P-450 per hr) for amobarbital, hexobarbital, and pentobarbital were 0.24 and 89, 0.19 and 345, and 0.25 and 100, respectively. The addition of NADH to reaction mixtures containing a NADPH-generating system increased the maximum velocities of amobarbital, hexobarbital, and pentobarbital by 77, 249, and 47%, respectively. The binding of the barbiturates to cytochrome P-450, expressed as binding constants (K8), were about one order of magnitude lower than the Michaelis constants for the hydroxylation of the barbiturates. Amobarbital, hexobarbital, and pentobarbital stimulated NADPH-cytochrome P-450 reductase activity by 2.9, 4.6, and 2.0 nmol of cytochrome P-450 reduced per min. Copyright © 1973 by The American Society for Pharmacology and Experimental Therapeutics