Common characteristics of the cytochrome P-450 system involved in 18- and 11β-hydroxylation of deoxycorticosterone in rat adrenals

• Main Authors: I Björkhem, K E Karlmar
• Format: Article
• Language: English
• Published: Elsevier 1977-09-01
• Series: Journal of Lipid Research
• Subjects: cholesterol side chain cleavage; mass fragmentography
• Online Access: http://www.sciencedirect.com/science/article/pii/S0022227520416013

18- and 11β-Hydroxylation of deoxycorticosterone and side chain cleavage of cholesterol were studied in mitochondria and submitochondrial reconstituted systems prepared from rat and bovine adrenals. A mass fragmentographic technique was used that allows determination of hydroxylation of both exogenous and endogenous cholesterol. The following results were obtained.(1) Treatment of rats with excess potassium chloride in drinking fluid increased mitochondrial cytochrome P-450 as well as 18- and 11β-hydroxylase activity in the adrenals. Cholesterol side chain cleavage was not affected. In the presence of excess adrenodoxin and adrenodoxin reductase, cytochrome P-450 isolated from potassium chloride-treated rats had higher 18- and 11β-hydroxylase activity per nmol than cytochrome P-450 isolated from control rats. The stimulatory effects on 18- and 11β-hydroxylation were of similar magnitude.(2) Long-term treatment with ACTH increased cholesterol side chain cleavage in the adrenals but had no effect on 18- and 11β-hydroxylase activity. The amount of cytochrome P-450 in the adrenals was not affected by the treatment. It was shown with isolated mitochondrial cytochrome P-450 in the presence of excess adrenodoxin and adrenodoxin reductase that the effect of ACTH was due to increase of side chain cleavage activity per nmol cytochrome P-450. Side chain cleavage of exogenous cholesterol was affected more than that of endogenous cholesterol.(3) Gel chromatography of soluble cytochrome P-450 prepared from rat and bovine adrenal mitochondria yielded chromatographic fractions having either a high 18- and 11β-hydroxylase activity and a low cholesterol side chain cleavage activity or the reverse. The ratio between 18- and 11β-hydroxylase activity was approximately constant, provided the origin of cytochrome P-450 was the same.(4) Addition of progesterone to incubations of deoxycorticosterone with soluble or insoluble rat adrenal cytochrome P-450 competitively inhibited 18- and 11β-hydroxylation of deoxycorticosterone to the same degree. Addition of deoxycorticosterone competitively inhibited 11β-hydroxylation of progesterone with the same system. Progesterone was not 18-hydroxylated by the system.From the results obtained, it is concluded that 18- and 11β-hydroxylation have similar properties and that the binding site for deoxycorticosterone is similar or identical in the two hydroxylations. The possibility that the same specific type of cytochrome P-450 is responsible for both 18- and 11β-hydroxylation of deoxycorticosterone is discussed.