Reconstituted liver microsomal enzyme system that hydroxylates drugs, other foreign compounds, and endogenous substrates. IX. The formation of a 455-nm metabolite-cytochrome P-450 complex

The reconstituted liver microsomal hydroxylation system was used to study the formation of a metabolite-cytochrome P-450 complex absorbing maximally at 455 nm, with benzphetamine and N-hydroxyamphetamine as substrates. Complex formation required the presence of NADPH, substrate, NADPH-cytochrome c reductase, lipid, and cytochrome P-450, indicating that metabolism of the substrate is essential. In the presence of fixed amounts of lipid and NADPH-cytochrome c reductase, the rate of complex formation with cytochrome P-450 isolated from phenobarbital-treated rats was much greater than that observed with cytochrome P-48 from 3-methylcholanthrene-treated rats or rabbits. These results are consistent with recent studies indicating that different forms of cytochrome P-450 with distinct spectral, catalytic, and immunological properties exist in liver microsomes.

Liver microsomal expoxide hydrase. Solubilization, purification, and characterization

Epoxide hydrase was solubilized from liver microsomes of phenobarbital-treated rats by treatment with cholate and purified to apparent homogeneity by ammonium sulfate fractionation and column chromatography in the presence of the nonionic detergent Emulgen 911 on DEAE-cellulose and hydroxylapatite. The purified enzyme preparation had a single major band with a molecular weight of 53,000 to 54,000 on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Other studies indicated that in the absence of sodium dodecyl sulfate, purified epoxide hydrase exists as high molecular weight aggregates. The preparation was essentially free of heme and flavin, but still contained small amounts of lipids and Emulgen 911.

Multiple forms of cytochrome P-450 in phenobarbital- and 3-methylcholanthrene-treated rats. Separation and spectral properties

Multiple forms of liver microsomal cytochrome P-450 isolated from immature male rats pretreated with phenobarbital or 3-methylcholanthrene are described. Afraction of low specific content (Fraction A. 1.7 TO 4.0 nmol of cytochrome P-450 per mg of protein) and a fraction substantially purified (Fraction B, 9.0 TO 11.0 NMOL of cytochrome P-450 per mg of protein) are obtained by DEAE-cellulose chromatography of a partially purified cytochrome P-450 preparation in the presence of Emulgen 911. Shifts in the absorption maxima in the CO-reduced and ethyl isocyanide difference spectra are observed in the fractions derived from 3-methylcholanthrene-treated rats. The fractions derived from phenobarbital-treated rats exhibit different 455:430 ratios and pH intercepts in the ethyl isocyanide difference spectra. The absolute oxidized spectra and n-octylamine binding spectra at room temperature and EPR analysis at the temperature of liquid helium characterize all the fractions, except the Fraction A from 3-methylcholanthrene-treated rats, as low spin ferric hemeproteins. The A hemeprotein fractions from both 3-methylcholanthrene- and phenobarbital-treated rats have poor catalytic activity for the metabolism of benzphentamine and 3,4-benzo-[a]pyrene in comparison to the B hemeprotein fractions which may be due to the presence of a high concentration of Emulgen 911 in the A fractions. However, the presence of Emulgen 911 cannot account for the spectral differences among the fractions.

Partial purification and separation of multiple forms of cytochrome. P-450 and cytochrome P-448 from rat liver microsomes

1. Partial purification of liver microsomal cytochrome p-450 results in the separation of two forms of cytochrome p-450 from phenobarbital-treated rats and two forms of cytochrome p-44, from 3-methylcholanthrene-treated rats. 2. Each of the four cytochrome fractions had different spectral properties (absolute spectra, CO differences spectra, and ethylisocyanide difference spectra). 3. The hemeprotein in fractions which elute from a DEAE-cellulose column at 100 mKM KCl fraction IV B) are more highly purified than the hemeproteins (fraction IV A) that elute in the column volume. 4. The more highly purified cytochrome fractions (IV B) contain 9-11 moles of cytochrome P-450 or P-448 per mg protein (an approximately 5-7 fold purification over microsomes) and are enzymatically active in the metabolism of a variety of substrates when combined with lipid and NADPH-cytochrome c reductase. These hemeprotein fractions are free of cytochrome b5 and NADPH-cytochrome c reductase, and the hemeproteins are purified approximately 100-fold with respect to phospholipid. The cytochrome P-450 and P-448 are virtually free of epoxide hydrase.

The uptake of radioactive copper by the brain and other tissues of the developing rat

1.64Cu as copper chloride in aqueous solution was given by intraperitoneal injection to rats varying in age from a few hours to 14 weeks. The isotope was allowed to circulate in the body for 24 h.

2. The amount of gamma radioactivity present in the brain and blood was measured and the percentage of the initial dose present was calculated. It was shown that the brain64Cu activity reached a maximum around the 16th day of life and that the blood showed a steady decrease in the64Cu activity per g from birth to maturity. Measurements were also made on the liver and kidney.

3. The excretion of64Cu in the urine and faeces in 24 h was also studied. Approximately 30% of the isotope was excreted in that time, mostly in the faeces.

4. A limited number of experiments in three different age groups were carried out to discover whether changes in specific activity of the isotope given to rats had a significant effect on the percentage of64Cu taken up by the brain and blood. No such effect was seen.