Benzo Pyrene Hydroxylase Research Articles

Varying effect of phenobarbital on hepatic drug metabolism in rats of different ages

The developmental pattern of benzo(a)pyrene hydroxylase and ethylmorphine N-demethylase from 8 days before birth up to 100 days of age in rat liver homogenate was investigated. These two drug metabolizing enzyme reactions exhibited their highest activities at different times of hepatic development. Treatment with phenobarbital produces a selective effect on the magnitude of stimulation of these two enzyme reactions in rats of different ages. The higher levels of drug metabolizing enzyme activity after phenobarbital treatment were not always paralleled by higher liver weights. The duration of hexobarbital hypnosis was longer in young than in adult rats. However, after phenobarbital treatment hexobarbital effectiveness was decreased more in young than in adult rats.

The effect of dietary protein and fat on the activity of aryl hydrocarbon hydroxylase in rat liver, kidney and lung

Feeding low protein diets reduces the activity of aryl hydrocarbon hydroxylase (3,4 benzo(α)pyrene hydroxylase) in rat liver and lung, but not in the kidney. In the kidney the level of aryl hydrocarbon hydroxylase activity is increased by feeding a diet containing fats. This increase in the kidney aryl hydrocarbon hydroxylase activity occurs when the fat content of the diet rises above 4 per cent and is maximal after feeding such diets for 7 days.

Induction of microsomal aryl hydrocarbon (3,4-benzo(α)pyrene) hydroxylase and cytochrome P-450 k in rat kidney cortex : II. Interactions with the induced hemoprotein

Benzo(α)pyrene treatment resulted in stimulation of only cytochrome P-450 K and benzo(α)pyrene hydroxylase activity in rat kidney cortex microsomes. Spectral properties of cytochrome P-450 K showed that the 452 nm peak of the reduced hemoprotein CO-complex was not shifted in benzo(α)pyrene-treated rats. The off-balance absolute spectrum of oxidized cytochrome P-450 K displayed an absorption maximum at 414 nm, another band at 385 nm, and a distinct shoulder at 398 nm. Addition of benzo(α)pyrene to kidney microsomes resulted in a type I spectral change seen only in benzo(α)pyrene-treated rats. The addition of ethyl isocyanide to dithionitetreated microsomes from control rats gave rise to two Soret peaks, 432 nm and 458 nm. These peaks were proportionately increased in benzo(α)pyrene-treated rats; furthermore, the 458 nm peak was not shifted. The relative heights of the two peaks were in a pH-dependent equilibrium similar to that observed in liver; however, in contrast to liver, the pH, at which the ratio of the peak heights equals one, was the same for both benzo(α)pyrene-treated and control microsomes. These data indicate that the newly induced hemoprotein has spectral properties markedly different from those of the benzo(α)pyrene-induced liver hemoprotein, yet similar to those of the “noninduced” kidney hemoprotein. α-Naphthoflavone, an inhibitor of the aryl hydroxylase system, induced a type I spectral change, suggesting the mode of action of α-naphthoflavone to be its interaction with cytochrome P-450 K probably at or near the active site. Finally, the rate of reduction of cytochrome P-450 K was not affected by the presence of benzo(α)pyrene.

Effect of spironolactone and ethylestrenol on benzo(a)pyrene hydroxylase (EC 1.14.1.1) and other chemical constituents of hepatic microsomes.

In rats, spironolactone and ethylestrenol, like phenobarbital, enhance the NADPH-dependent hydroxylation of benzo(a)pyrene in the hepatic microsomal plus supernatant fraction and increase liver weight and microsomal phospholipid content as well as NADPH cytochrome c reductase and diaphorase activities, but only ethylestrenol and phenobarbital influence the microsomal protein content and cytochrome P-450 level.Neither spironolactone, ethylestrenol, nor phenobarbital affects NADH cytochrome c reductase and diaphorase activities, and only phenobarbital alters the cytochrome b5 level.These findings indicate that, while both the steroids and phenobarbital stimulate microsomal mixed-function oxidation, there are qualitative and quantitative differences between their action.

Mixed-function oxidation in tumors.

Liver microsomes of the rat contain a group of hydroxylating enzymes which are coupled to a greater or lesser degree to the electron flow system. In our studies, enzymes believed to be directly associated with the electron flow chain of NADPH, ferricyanide reduction, cytochrome c, cytochrome P-450 and substrate hydroxylation have been observed in livers obtained from normal, tumor-bearing and whole body irradiated rats as well as in Morris hepatoma 7777 and dimethyl-amino-biphenyl induced breast tumors.A significant difference appeared to exist in the activity of NADPH oxidase, NADP-ferricyanide reductase and benzopyrene hydroxylase when normal liver was compared with the liver obtained from a breast-tumor-bearing animal. Both cytochrome P-450 and cytochrome b(5) were decreased in the tumor-bearing animal.Tissue distribution of benzopyrene hydroxylase in normal, lactating and tumor-bearing Wistar rats has been studied.With the exception of NADPH oxidase, the activities of NADP-cytochrome c reductase, NADPH-ferricyanide reductase, benzopyrene hydroxylase and P-450 were markedly different in liver from Morris hepatoma 7777-bearing Buffalo rat when this was compared with homologous tissue obtained from normal Buffalo rat.Whole-body irradiated animals showed increased P-450 and NADPH oxidase activity in liver as a function of irradiation and there further appeared to be a correlation with decreased ferricyanide reductase activity.