The enzyme system in liver microsomes which catalyzes the w-hydroxylation of fatty acids in the presence of molecular oxygen and a reduced pyridine nucleotide has been solubilized and resolved into fractions containing cytochrome P-450, a cytochrome P-450 reductase, and a heat-stable factor. The apparent K, values of TPNH and DPNH are 2.0 x 10m5 M and 6.3 X 10e4 M, respectively. As a further in...

The 7a-hydroxylation of taurodeoxycholic acid and the 6&hydroxylation of taurochenodeoxycholic acid and lithocholic acid were studied with a reconstituted system from rat liver microsomes consisting of partially purified cytochrome P-450, NADPH-cytochrome P-450 reductase, a synthetic phosphatidylcholine and NADPH or an NADPH-generating system. 7a-Hydroxylase activity was observed with cytochrom...

The administration of 3-methylcholanthrene to rats leads to changes in the enzyme systems of the liver which oxidize drugs. These changes have been related to changes in some of the spectral properties of microsomal cytochrome P-450. The altered cytochrome appearing after 3-methylcholanthrene treatment has been called P,-450,’ P-448, P-446, Pa450, and high-spin P-450 by different investigators....

NADPH-cytochrome P-450 oxidoreductase (CPR) is essential for the catalytic activity of cytochrome P-450 (P-450). On a molar basis, the amount of P-450 exceeds that of CPR in human liver. In this study, we investigated whether drug-drug interactions can occur as a result of competition between P-450 isozymes for this ancillary protein. For this purpose, combinations of P-450 isozymes were coexpr...

Seven isozymes of cytochrome P-450 were tested to establish whether they could N-oxidize azoprocarbazine to form the two isomeric azoxy metabolites after optimizing the reconstitution of various purified isozymes with regard to substrate concentration, exogenous lipid, and reduced nicotinamide adenine dinucleotide phosphate-cytochrome c (P-450) reductase concentration. Two isozymes, cytochromes...

The interactions between purified rat hepatic m rosomal cytochrome P-450 and the type I ligands benzphetamine and cytochrome b6 have been studied in the presence of phospholipid using difference spectrophotometry. Cytochrome bs was shown to interact with cytochrome P-450 to form a tight 1:1 complex (Kd = 275 nM), in which the proportion of high spin cytochrome P-450 was increased from 7 to 30%....

The role of TPNH as the donor of reducing equivalents to microsomal mixed function oxidations of drugs, other foreign compounds, and steroids in the liver is well established (1-5). DPNH will not substitute for TPNH in the cyt#{243}chrome P-450-mediated oxidation of drugs, but reaction rates are increased when both nucleotides are present (61 1 ). Although this synergistic role of DPNH has been...

1. A new microsomal preparation, obtained from whole houseflies is described in terms of its cytochrome P-450 content and its hydroxylating activity. 2. Microsomes prepared from whole-fly brei, obtained with the aid of a mortar (a procedure that avoids the destruction of sarcosomes), contain 0.265nmol of cytochrome P-450 and hydroxylate naphthalene at a rate of 28.5nmol/mg of microsomal protein...