Purification and properties of cytochrome p-450 (11beta- and 18-hydroxylase) from bovine adrenocortical mitochondria

Purification of cytochromes P-450(scc) and P-450(17 alpha) by steroid-binding affinity column chromatography

The preparation, testing and use of a variety of cholesterol-, deoxycorticosterone (DOC)- and pregnenolone-binding 1,6-diaminohexyl (EAH)-Sepharose 4B supports for affinity column chromatography of cytochromes P-450(scc) and P-450(17 alpha) from bovine adrenal and pig testis are described. EAH-Sepharose 4B has free amino groups at the end of a 10-atom spacer arm. Hydroxyl groups of cholesterol (3 beta), deoxycorticosterone (21 beta) and pregnenolone (3 beta) are linked to succinic anhydride in pyridine through an ester linkage. These coupling ligands of hemisuccinate were synthesized by a general procedure. Free amino groups of EAH-Sepharose 4B were used to couple ligands, containing carboxyl groups, by the carbodiimide coupling method. Both the purified cytochromes P-450(scc) and P-450(17 alpha) were found to be homogeneous and estimated to have a molecular weight of 52,000 on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The carbon monoxide difference spectra with peaks at 450 and 448 nm exhibit the absorption spectra of typical cytochromes P-450(scc) and P-450(17 alpha), respectively. Cytochromes P-450(scc) and P-450(17 alpha) were determined to have isoelectric points of 8.0 and 6.5 in isoelectric focusing on a pH gradient gel. Cytochrome P-450s can be purified between 425- and 1000-fold from the crude extracts.

Inhibition of aldosterone formation by cortisol in rat adrenal mitochondria

In this work we confirm by a metabolic method the existence of at least two enzymes with 11 beta- and 18-hydroxylase activities in rat adrenal mitochondria. The method was based on the ability of cortisol (F), a foreign alternative substrate, to inhibit competitively metabolite productions from various precursors. F inhibited a) aldosterone (ALDO) production from 11-deoxycorticosterone (DOC) without affecting the yields of corticosterone (B) and 18-hydroxy-11-deoxycorticosterone (18-OHDOC); b) 18-hydroxycorticosterone and aldosterone productions from B (Ki = 2.5 +/- 0.5 microM); and c) ALDO production from 18-OHDOC. These results suggest the existence of two categories of enzymes with both 11 beta- and 18-hydroxylase activities, one comprising those that catalyze the conversions of DOC to B and 18-OHDOC (F-insensitive reactions [FIS]) and the other one comprising the enzymes involved in the conversions of B to 18-OHB and ALDO and that of 18-OHDOC to ALDO (F-sensitive reactions [FS]). The cloned enzymes CYP11B1 and CYP11B2 would pertain respectively to the FIS and FS categories.

19-Nor-corticosteroids in genetic hypertension. Effects of inhibitors of 11 beta, 18, 19-hydroxylase activity

The long-term objective is to understand the role of the adrenal in altering systemic arterial blood pressure. This paper summarizes research on genetic hypertension in the rat and bears a relationship to several forms of human hypertension in which defects of steroid hydroxylases lead to increased secretion of mineralocorticoids other than aldosterone in genetic and experimental hypertension in rats. We demonstrated that 19-nor-corticosteroids are produced in excess in genetic and experimental hypertension in rats and man. We studied the enzymatic alteration responsible for excessive production of 19-nor-deoxycorticosterone (19-nor-DOC) in the salt-sensitive hypertensive rat S/JR. Biosynthesis of 19-nor-steroids involves hydroxylation of the C-19 methyl group. We characterized the adrenal 11 beta, 18,19-hydroxylase enzyme system in inbred salt-sensitive and resistant rats (R/JR). This system is capable of all three hydroxylations. The Km for 19-hydroxylation was different from S/JR and R/JR but was much greater for 11 beta- and 18-hydroxylation in both. This suggested that the catalytic site for 19-hydroxylation is different from that for 11 beta and 18. The S/JR adrenal enzyme binds the substrate with higher affinity than does the R/JR adrenal enzyme. We were unable to distinguish the cDNAs of the S/JR from the R/JR adrenal enzyme from bovine 11 beta-hydroxylase cDNA by restriction mapping. We were unable to demonstrate restriction length polymorphism. 19-Acetylenic DOC is an inhibitor which preferentially inhibits the 19-hydroxylation of DOC, and does not interfere with the 18- and 11 beta-hydroxylation. This inhibition leads to a reduction in blood pressure in the S/JR Dahl rat. We suggest that an S/JR 19-nor-DOC is involved in the development of salt-sensitivity and hypertension and that inhibition of its formation by acetylenic DOC and other aromatase and non-aromatase inhibitors is associated with reversal of these phenomena.

Characterization of the adrenal 11 beta-hydroxylase in inbred salt-sensitive and resistant rats

Rats have been bred for susceptibility and resistance to the hypertensive effect of dietary salt (S/JR & R/JR). S/JR have an abnormal adrenal steroid 11 beta,18-hydroxylase activity resulting in increased production of 18-OH-DOC. S/JR also produce increased quantities of 19-nor-DOC, which may be related, since the 11 beta,18-hydroxylase also catalyzes the 19-hydroxylation of DOC, a pivotal step in 19-nor-DOC biosynthesis. The purpose of the present studies was to further characterize the mutant S/JR adrenal steroid 11 beta,18-hydroxylase. Preliminary studies are also presented on assessing the renal 19-desmolase, the last step in 19-nor-DOC biosynthesis. Adrenal glands were harvested from R/JR and S/JR and prepared for incubation studies, protein immunoblotting, and RNA analysis. Kidneys from Sprague-Dawley rats were also used for isolated renal perfusion studies. Both S/JR and R/JR strains had a single immunostaining band for 11 beta,18-hydroxylase at 51,000 molecular weight which were equal in intensity. Both strains had a single RNA transcript at 4.3 kilobases which hybridized with equal intensity to the bovine cDNA (pB11-9). The Km for 11 beta- and 18-hydroxylation was identical within strains but was different between strains. The Km for 19-hydroxylation was different between S/JR and R/JR, and was much greater than 11 beta- and 18-hydroxylation in both strains. This suggests that the catalytic site for 19-hydroxylation is different than that for 11 beta- and 18-hydroxylation and that the S/JR enzyme binds the substrate with higher affinity than the R/JR enzyme. In the isolated perfusion studies the rat kidneys converted 80% of 19-oxo-DOC to either 19-oic-DOC or 19-nor-DOC. These data demonstrate that the difference in S/JR enzyme activity is probably due to a point mutation in the enzyme or to a change in a regulatory protein.

Incorporation of steroidogenic pathways which produce cortisol and aldosterone from cholesterol into nonsteroidogenic cells

Cortisol production from cholesterol requires the activity of four steroid hydroxylases: cholesterol side chain cleavage cytochrome P-450 (P-450scc), 17 alpha-hydroxylase cytochrome P-450 (P-45017 alpha), 21-hydroxylase cytochrome P-450 (P-450C21) and 11 beta-hydroxylase cytochrome P-450 (P-45011 beta). We have previously shown that transformed, nonsteroidogenic COS 1 cells derived from monkey kidney are a useful system for expression of various forms of cytochrome P-450. The present study shows that COS 1 cell cultures multiply transfected with six plasmids containing all four steroid hydroxylases, 3 beta-hydroxysteroid dehydrogenase/delta 5----4-isomerase (3 beta HSD) and adrenodoxin produce cortisol and aldosterone when 22(R)-hydroxycholesterol is supplied to the system. When pregnenolone is used as substrate, various intermediate metabolites are detected at different time points further establishing the incorporation of complete functional steroidogenic pathways into the nonsteroidogenic cell cultures. Since the first and the last reactions in these pathways take place in the mitochondrion, the movement of various intermediate metabolites from mitochondrion to endoplasmic reticulum and back to mitochondrion occurs in and between COS 1 cells.

Inhibition of hamster adrenal 11 beta/19-hydroxylase activity

Increased mineralocorticoid activity has been associated with elevated urinary levels of 19-nordeoxycorticosterone in several forms of experimental and human hypertension. Biosynthesis of 19-norsteroids involves hydroxylation of the C-19 methyl group. We synthesized the 4-hydroxy analogs of deoxycorticosterone, deoxycorticosterone acetate, progesterone, and androstenedione and evaluated them as inhibitors of deoxycorticosterone 11 beta/19-hydroxylase using hamster adrenal mitochondrial preparations. These 4-hydroxy analogs were inhibitors of this P 450 hydroxylase, with approximately 10 times weaker affinity than their respective natural substrates. 4-Hydroxydeoxycorticosterone was the most potent inhibitor evaluated in this study. The half-maximal inhibitory concentration of deoxycorticosterone hydroxylation was 5 microM, 15 microM, more than 50 microM, and 14 microM, respectively, for the above compounds.

18-Hydroxylase activity in the Y1 adrenal cell line

18-Hydroxylase activity, reported here for the first time in the mouse adrenal tumor cell line (Y1), was expressed in the metabolism of 11-deoxycorticosterone (DOC) and corticosterone (B). Detected after 24 h of incubation, it was more evident after 48 h and produced mostly 18-hydroxy-20 alpha-DHB from these exogenous substrates. However, 18-hydroxylation was quantitatively less significant than the metabolism of 20 alpha-reduction and 11 beta-hydroxylation (of DOC). The latter is also the predominant metabolism of progesterone in this cell line, during the conversion of cholesterol from the serum-supplemented culture media. The cytochrome P-450 11 beta activity of the Y1 cells is similar to that of the mouse in vivo which catalyzes the production of an 11 beta 18-dihydroxylated metabolite as the principal 18-hydroxylated steroid. It is different from that of other species, such as the rat and the bovine, both in terms of the ratio of 11 beta- to 18-hydroxylated metabolites and of the structure of these metabolites.

Cytochromes P-450 in steroidogenesis: are these enzymes more specific than those of drug metabolism?

1. In contrast to drug-metabolizing cytochromes P-450, the corresponding steroidogenic enzymes appear to be highly specific with respect to substrates, reactions catalysed, and the sites in the substrate molecule that are attacked. 2. Recent studies have shown that important exceptions to this generalization are encountered. 3. The conversion of 11-deoxycorticosterone to aldosterone requires three enzymatic reactions, the last of which (aldehyde synthetase), like the first two, requires a P-450 mono-oxygenation. The involvement of P-450 in this third step (from alcohol to aldehyde) was demonstrated by photochemical action spectra and determination of stoichiometry. The three reactions were shown to be catalysed by a single enzyme as demonstrated by immunoprecipitation and the use of a homogenous enzyme. 4. The conversion of pregnenolone and progesterone to the corresponding delta 16-C19 steroids, which are pheromones, is catalysed by a cytochrome P-450 that also catalyses the conversion of progesterone to androstenedione (that is, C21 side-chain cleavage; hydroxylase/lyase). The synthesis of the delta 16 compounds requires cytochrome b5. 5. The conversion of testosterone and epitestosterone to androstenedione is catalysed by P-450b. Studies of kinetic isotope effects using deuterium and 18O2 show that P-450b catalyses this reaction with epitestosterone via the formation of a gem diol, whereas, with testosterone as substrate, one-third of the product is formed via the same mechanism while the remainder results from the mechanism described as dual hydrogen abstraction.

Conversion of 11-deoxycorticosterone and corticosterone to aldosterone by cytochrome P-450 11 beta-/18-hydroxylase from porcine adrenal

Highly purified cytochrome P-450 11 beta-/18-hydroxylase and the electron carriers adrenodoxin and adrenodoxin reductase were prepared from porcine adrenal. When the enzyme was incubated with the electron carriers, 11-deoxycorticosterone (DOC) and NADPH, the following products were isolated and measured by HPLC: corticosterone, 18-hydroxy-11-deoxycorticosterone (18-hydroxyDOC), 18-hydroxycorticosterone and aldosterone. All of the DOC consumed by the enzyme can be accounted for by the formation of these four steroids. Aldosterone was identified by mass spectroscopy and by preparing [3H]aldosterone from [3H]corticosterone followed by recrystallization at constant specific activity after addition of authentic aldosterone. Corticosterone and 18-hydroxycorticosterone were also converted to aldosterone. Conversion of corticosterone and 18-hydroxycorticosterone to aldosterone required P-450, both electron carriers, NADPH and substrate. The reaction is inhibited by CO and metyrapone. Moreover, all three activities of the purified enzyme decline at the same rate when the enzyme is kept at room temperature for various periods of time and when the enzyme is treated with increasing concentrations of anti-11 beta-hydroxylase (IgG) before assay. It is concluded that cytochrome P-450 11 beta-/18-hydroxylase can convert DOC to aldosterone via corticosterone and 18-hydroxycorticosterone. The stoichiometry of this conversion was found to be 3 moles of NADPH, 3 moles of H+ and 3 moles of oxygen per mole of aldosterone produced.

Gerbil adrenal 11 beta- and 19-hydroxylating activities respond similarly to inhibitory or stimulatory agents: two activities of a single enzyme

A high level of steroid 19-hydroxylation is exhibited by adrenal mitochondria of the gerbil, Meriones, unguiculatus, that accounts for the ability of that species to produce nearly equal amounts of corticosterone and 19-hydroxycorticosterone (Proc. Soc. exp. Biol. Med. 165 (1980) 69-74). Inhibitors of steroidogenesis and a polyclonal antibody against bovine cytochrome P-450(11 beta) were used to determine if the agents would effect differential or parallel suppression of 19- vs 11 beta-hydroxylation by gerbil adrenal mitochondria in vitro. The inhibitors (0.1-60 microM) tested (listed in order of decreasing effectiveness) were imazalil, metyrapone, miconazole and 4-hydroxyandrostenedione. With each inhibitor the degree of suppression of 11 beta-hydroxylation was accompanied by a parallel decline in 19-hydroxylation. The addition of the polyclonal antibody preparation also produced equivalent declines in the rates of the two hydroxylation reactions. The addition of ACTH 1 microM to primary cultures of gerbil adrenal cells brought about nearly equal increases in the secretion of 11 beta- and 19-hydroxylated steroids into the culture media. These results support the hypothesis that the 11 beta-hydroxylase of gerbil adrenal mitochondria has the capacity to carry out 11 beta- and 19-hydroxylations with nearly equal facility.

Immunogold cytochemistry of cytochromes P-450 in porcine adrenal cortex. Two enzymes (side-chain cleavage and 11 beta-hydroxylase) are co-localized in the same mitochondria

In order to study the distribution of mitochondrial cytochromes P-450 in porcine adrenal glands, the glands of anesthetized pigs were fixed in situ. Polyclonal antibodies against two cytochromes P-450, i.e., C27 side-chain cleavage enzyme and 11 beta-hydroxylase, were used to study the distribution of these enzymes in cryosections of the adrenal cortex. Ultrathin cryosections were evaluated by both protein-A/gold/silver immunocytochemistry and immunoelectron microscopy using double labeling with protein-A/colloidal-gold. At light microscopy, the two cytochrome P-450 enzymes were found to be broadly distributed in both the fasciculata and glomerulosa zones of the adrenal cortex. Quantitative immunoelectron microscopy revealed that both enzymes were localized only in mitochondria, in which they were present on the inner aspects of the inner mitochondrial membrane. Both cytochromes P-450 were demonstrable in all of the mitochondria examined, and statistical evaluation of the ratios of the two enzymes present in individual mitochondria yielded a normal distribution curve. Since no evidence was found for the preferential localization of either enzyme in a special population of mitochondria, we conclude that all mitochondria of the adrenal cortex contain both enzymes. We discuss implications of these findings with respect to the regulation of steroidogenesis.

Structure of genes encoding steroidogenic enzymes

Synthesis of adrenal steroid hormones from cholesterol entails the actions of only five enzymes, four of which are specific forms of cytochrome P450. These cytochrome P450 enzymes have all been isolated and their activities reconstituted in vitro, showing that each enzyme catalyses multiple steroidal conversions. Genes or complementary DNAs have been cloned for human P450scc (the cholesterol side-chain cleavage enzyme), P450c17 (17 alpha-hydroxylase/17,20 lyase) and P450c21 (21-hydroxylase). The sequences for microsomal P450c17 and P450c21 are much more closely related to one another than either is to the sequence for mitochondrial P450scc. Each of these P450 enzymes is encoded by a single human gene; the gene for P450scc lies on chromosome 15, that for P450c17 lies on chromosome 10, and that for P450c21 lies on chromosome 6. The human, mouse and bovine genomes each have two P450c21 genes. While only one of these is active in mouse and man, both genes may be active in cattle. A wide variety of lesions in the human P450c21(B) gene causes congenital adrenal hyperplasia, a common genetic disorder.

Preparation and characterization of submitochondrial fractions from adrenal cells

A method for preparing submitochondrial fractions from adrenocortical cells was developed by adapting a procedure that has been successful with yeast mitochondria. The method is based upon osmotic swelling, sonication and centrifugation in sucrose. The preparation yields highly purified fractions of outer membrane, intermembrane space, inner membrane and a less purified fraction of matrix. Recoveries are good so that 10(7) cells yield approximately 170 micrograms of inner membrane protein and 12 micrograms of outer membrane protein. Electron microscopy shows that the outer membrane fraction consists of vesicles (0.2-0.6 micron diameter) while inner membrane appears as densely packed sheets of membranous material. Two-dimensional polyacrylamide gels (isoelectric focusing followed by electrophoresis) of all the fractions give highly reproducible patterns of protein spots with Coomassie staining. Steroidogenic proteins were found only in inner membrane fractions which were shown to contain cytochrome P-450 C27 side-chain cleavage and P-450 11 beta-hydroxylase together with adrenodoxin and adrenodoxin reductase. Inner membrane catalyzes side-chain cleavage of cholesterol (conversions to pregnenolone) and 11 beta-hydroxylation (DOC----corticosterone) when substrate and NADPH are added. The preparation yields highly purified submitochondrial fractions from Y-1 mouse adrenal tumor cells and from porcine and bovine adrenocortical mitochondria. The method has the virtue of yielding highly purified intermembrane fluid which is not true of other methods for fractionation of adrenal mitochondria. The procedure also yields cleaner preparations of the two membranes than two other published methods currently used to prepare submitochondrial fractions from adrenocortical cells.

Purification to homogeneity of aromatase from human placenta

Aromatase cytochrome P-450 has been purified from human placenta to homogeneity, as demonstrated by electrophoresis on polyacrylamide gels with SDS, and by double diffusion against an antibody raised in rabbits. The enzyme converts androstenedione to estrone (Vmax 13.3 n moles/min/n mole P-450; Km 30 microM) and testosterone to estradiol. Aromatase activity requires P-450, P-450 reductase and NADPH. Enzyme activity is inhibited by anti-aromatase antibodies and by 4-hydroxyandrostenedione. The enzyme shows a molecular weight of 55,000, is extremely unstable and spontaneously forms P-420 with a half-life of 2.5 days.

18,19-Dihydroxydeoxycorticosterone, a new metabolite produced from 18-hydroxydeoxycorticosterone by cytochrome P-450(11) beta. Chemical synthesis and structural analysis by 1H NMR

A new metabolite was produced from 18-hydroxydeoxycorticosterone by the cytochrome P-450(11) beta linked hydroxylase system purified from bovine adrenocortical mitochondria. It was identified as 18,19-dihydroxydeoxycorticosterone by chemical synthesis on the basis of high-performance liquid chromatography, gas chromatography-mass spectrometry, and proton nuclear magnetic resonance (1H NMR) spectroscopy, and detailed structural analysis of it was performed by 1H NMR spectroscopy. The methylene protons at the C-19 position of the steroid were nonequivalent and coupled with each other, having a coupling constant of 10.6 Hz. These protons had different coupling constants, 6.7 and 3.4 Hz, for the hydroxy proton at the C-19 position. Due to these couplings, the signals of the methylene protons were observed around 3.9 ppm as two double doublets. The methylene protons at the C-21 position were also nonequivalent, having a coupling constant of 11.1 Hz. Coupling constants between these methylene protons and the hydroxy proton at the C-21 position were 8.2 and 4.2 Hz, respectively. These results indicate that both hydroxymethyl groups at the C-19 and C-21 positions do not freely rotate in chloroform solution. The signals of hydroxy protons at the C-19 and C-21 positions were found at 1.25 and 1.87 ppm, respectively, by means of decoupling of the corresponding methylene protons. The hydroxy proton at the C-18 position was found to scarcely couple with any proton. This fact suggests that this hydroxy group is linked to the C-20 position, making a hemiketal bridge between the C-18 and the C-20.

Aldosterone biosynthesis by a reconstituted cytochrome P-45011 beta system

[3H]Corticosterone was incubated with cytochrome P-45011 beta purified to electrophoretic homogeneity from bovine adrenocortical mitochondria, and the reaction products were analyzed by high performance liquid chromatography. The production of aldosterone (21.2 pmol/nmol P-450/min) and 18-hydroxycorticosterone (1.17 nmol/nmol P-450/min) was observed. When lipidic extracts from mitochondria of bovine adrenocortical zona glomerulosa were added to the reaction mixture, the rate of production of aldosterone was increased 28-fold. When [3H]18-hydroxycorticosterone was incubated with cytochrome P-45011 beta, the amount of aldosterone produced was 55.7 pmol/nmol P-450/min in the absence of the lipidic extracts and the enhancing effect of the lipidic extracts was 4-fold.

Regulation of 18-hydroxycorticosterone formation in bovine adrenocortical mitochondria

The conversion of deoxycorticosterone to 18-hydroxycorticosterone was examined by using sonicated mitochondrial suspension of bovine adrenocortex. The KM's of deoxycorticosterone for the 11 beta- and 18-hydroxylations were in the same range (1 microM), while the turnover number for the 11 beta-hydroxylation (50 nmol/min/nmol cytochrome P-450) was 6 times as great as that for the 18-hydroxylation (7.3). The KM and turnover number for the 18-hydroxylation of corticosterone were 6 microM and 0.4, respectively. Those for the 11 beta-hydroxylation of 18-hydroxy-11-deoxycorticosterone were 120 microM and 5. When products were analysed in the incubation of deoxycorticosterone with the mitochondrial suspension containing a larger amount of cytochrome P-450, the formation of 18-hydroxycorticosterone was observed in addition to the formation of corticosterone and 18-hydroxy-11-deoxycorticosterone. The kinetic interrelation between the two pathways was further examined together with consideration of the cytochrome P-450-linked hydroxylation system. The result suggests that the pathway via 18-hydroxy-11-deoxycorticosterone substantially participates in the formation of 18-hydroxycorticosterone from deoxycorticosterone. The perturbation of this network by an artificial means, such as the addition of Triton X-100, revealed that the detergent (0.02%) facilitated the production of 18-hydroxycorticosterone from deoxycorticosterone, regardless of its inhibitory effect on the production of corticosterone and 18-hydroxy-11-deoxycorticosterone from deoxycorticosterone. These studies provide an important insight into the regulation mechanism of 18-hydroxycorticosterone formation from the precursors on the mitochondrial level.

Phosphorylation of purified mitochondrial cytochromes P-450 (cholesterol desmolase and 11 beta-hydroxylase) from bovine adrenal cortex

Two key steroidogenic mitochondrial cytochromes P-450 (cholesterol side-chain cleavage (scc) and 11 beta-hydroxylation (11 beta)) were purified from bovine adrenal cortex and examined as potential phosphorylatable substrates using purified cAMP-dependent protein kinase subunit (C) and A type (CKA) and G type (CKG) cAMP-independent casein kinases. Of the two cytochromes P-450, only P-450 11 beta was able to incorporate phosphate from ATP in the presence of C (Km = 7.5 microM), whereas CKA and CKG were ineffective. Phosphorylation of P-450 11 beta (maximum incorporation of 1 mole of 32P per mole of cytochrome, only on serine residues) did not modify the enzymatic activity of an 11 beta-hydroxylation system reconstituted in vitro from purified components, when adrenodoxin was in excess in the reaction. However, kinetic studies showed that P-450 11 beta phosphorylation strikingly increases the P-450 11 beta-adrenodoxin affinity in a phosphorylation-dependent manner. This would result in a net increase in 11 beta-hydroxylase activity under in vivo conditions where adrenodoxin availability is limited. Possible significance of these observations in the regulation of differentiated adrenocortical functions remains to be further examined.

Adrenal hydroxylations in genetically obese and hypertensive rats

The separate steps in the formation of aldosterone from cholesterol were studied in a strain of spontaneously hypertensive rats in which phenotypic obesity is inherited as a recessive trait (Koletsky rats). The obese and hypertensive state had little or no effect on side-chain cleavage of cholesterol, formation of progesterone from pregnenolone or 21-hydroxylation. Mitochondrial 18-hydroxylation of endogenous and exogenous corticosterone, however, as well as 18- and 11 beta-hydroxylation of deoxycorticosterone, were increased in obese hypertensive rats, both when compared with non-obese hypertensive siblings and when compared with healthy Sprague-Dawley rats. 18-Hydroxylation of corticosterone was increased more than 18-hydroxylation of deoxycorticosterone. In non-obese hypertensive rats, the adrenal content of mitochondrial cytochrome P-450 was lower than that in obese hypertensive rats but higher than that in rats of the conventional Sprague-Dawley strain. The results are discussed with respect to possible heterogeneity of adrenal cytochrome P-450 and to possible explanations for the changes observed.

Cytochrome P-450 from mitochondria of bovine adrenal cortex: comparison of cholesterol side-chain cleavage P-450 with steroid 11beta-hydroxylation P-450 and immunochemical cross-reactivity between adrenal mitochondrial and liver microsomal cytochromes P-450

Adrenocortical mitochondrial cytochrome P-450 specific to the cholesterol side-chain cleavage (desmolase) reaction differs from that for the 11beta-hydroxylation reaction of deoxycorticosterone. The former cytochrome appears to be more loosely bound to the inner membrane than the latter. Upon ageing at 0 degrees C or by aerobic treatment with ferrous ions, the desmolase P-450 was more stable than the 11beta-hydroxylase P-450. By utilizing artificial hydroxylating agents such as cumene hydroperoxide, H2O2, and sodium periodate, the hydroxylation reaction of deoxycorticosterone to corticosterone in the absence of NADPH was observed to a comparable extent with the reaction in the presence of adrenodoxin reductase, adrenodoxin and NADPH. However, the hydroxylation reaction of cholesterol to pregnenolone was not supported by these artificial agents. Immunochemical cross-reactivity of bovine adrenal desmolase P-450 with rabbit liver microsomal P-450LM4 was also investigated. We found a weak but significant cross-reactivity between the adrenal mitochondrial P-450 and liver microsomal P-450LM4, indicating to some extent a homology between adrenal and liver cytochromes P-450.

Cytochrome P-450 for 11beta- and 18-hydroxylase activities of bovine adrenocortical mitochondria: one enzyme or two?

The 11beta- and 18-hydroxylase activities of a highly purified cytochrome P-450 from bovine adrenocortical mitochondria have been examined in detail with a view to determining whether the two activities are shown by a single protein or by two distinct proteins. The purified enzyme shows a single N-terminal residue (glutamic acid) and its amino acid composition is reported. Both enzyme activities decay considerably during storage at 4 degrees C for 11 days and the rates of decay are similar for the two activities. Metyrapone inhibits both activities competitively (Ki = 1.50 and 1.43 micrometer for 11beta- and 18-hydroxylase, respectively). Carbon monoxide inhibits both activities and the ratio CO:O2 for 50% inhibition is similar for the two activities (K = 1.69 and 1.53). A variety of nonspecific inhibitors produce approximately the same inhibition of both activities. Finally, antiserum produced by rabbits to the purified enzyme on double diffusion in agarose gels gives a single band with the purified enzyme. Increasing concentrations of antiserum added to the assay system produce increasing and proportionate inhibition of both activities. The evidence strongly supports earlier suggestions that the two hydroxylase activities occur in a single protein.

Preparation and properties of side-chain cleavage cytochrome P-450 from bovine adrenal cortex by affinity chromatography with pregnenolone as ligand

A method is described for preparing cytochrome P-450 (side-chain cleavage) from bovine adrenocortical mitochondria, by affinity chromatography on pregnenolong-Sepharose beads. The cytochrome P-450 appears in two fractions, a large form of heterogeneous molecular weight (large P-450) and a form of molecular weight 850 000 composed of 16 apparently identical subunits (molecular weight 52 000-53 000); this form is referred to as protein 16. Electrophoresis on polyacrylamide gel yields one main band and two minor bands; the appearance of the gels is identical whether the starting material is large P-450 or protein 16 or protein 16 prepared by an entirely different method. Yields of protein 16 can be increased by rechromatography on pregnenolone-Sepharose of large P-450 made 0.1 mM in NADPH. Large P-450 shows greater than 10 heme groups per 16 subunits and is less active enzymatically than protein 16. Chromatography on Sepharose and analytical ultracentrifugation show that large P-450 is heterogeneous with respect to molecular weight. Protein 16 shows a heme content of 8 nmol/mg protein and for both large P-450 and protein 16 heme content by CO-difference spectroscopy is in agreement with values by pyridine hemochromogen. This method of preparing P-450 is convenient and both large P-450 and protein 16 are highly purified.