Incorporation of H<sub>2</sub><sup>18</sup>O into 20α, 22R‐di‐OH cholesterol: Evidence for an epoxide—diol pathway in the adrenocortical cholesterol side‐chain cleavage mechanism

Kraaipoel, R.J.; Degenhart, H. J.; Leferink, J.G.

doi:10.1016/0014-5793(75)80320-6

Cited by 23 publications

(5 citation statements)

References 14 publications

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“…Moreover, the purified enzyme preparations used in these studies [l] do not appear to contain epoxide hydratase activity. Our results do not support the mechanism of Kraaipoel et al [3,13,14] who do not give quantitative information on the relative efficiency of the conversion of their 20(22)-didehydrocholesterol (of unspecified stereochemistry) to pregenenolone, and consequently their experiments cannot be assessed fully. The transient putative epoxide intermediate detected on thin-layer chromatography [13] was claimed by these workers to be con- (Table 1) is low and does not vary with stereochemistry.…”

Section: Formution Of Pregnenolone From Cholesterol and Various Didehcontrasting

confidence: 98%

“…Recently, Kraaipoel and co-workers [3,13,14] observed that 20 (22)-didehydrocholesterol (compound 111 or IV, unspecified stereochemistry) markedly All steroid structures and their designation by Roman numerals are given in Fig. 1.…”

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confidence: 99%

“…They proposed an olefin-epoxide mechanism which is analogous in some ways to the olefin-epoxide intermediates in the dealkylation of fucosterol in insects [15]. The mechanism of Kraaipoel et al [3,13,14] In preliminary studies employing gas chromatography-mass spectrometry, Morisaki et al [ 161 were unable to detect significant conversion of any of the four isomeric 20,22-epoxycholesterols (compounds V -VIII) or of E-20(22)-didehydrocholesterol (compound I l l ) to pregnenolone by a highly purified sidechain cleavage enzyme system. Moreover, these putative intermediates did not trap any radioactivity from [3H]cholesterol in the enzyme systems that produced pregnenolone.…”

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confidence: 99%

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Biosynthesis of Pregnenolone from Cholesterol by Mitochondrial Enzymes of Bovine Adrenal Cortex. The Question of the Participation of the 20(22)-Olefins and 20,22-Epoxides of Cholesterol

et al. 1978

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The two isomeric 20(22)-olefins and the four isomeric 20,22-epoxides of cholesterol have been examined as possible intermediates in the conversion of cholesterol to pregnenolone both by crude extracts of acetone-dried bovine adrenal cortex mitochondria, and by a partially purified cytochrome P-450 specific for the side chain cleavage ( P -4 5 0~~~) .The quantities of pregnenolone (measured by radioimmunoassay) formed from these putative intermediates and from cholesterol, (2057-20-hydroxycholesterol, (22R)-22-hydroxycholesterol, and (20R,22R)-20,22-dihydroxycholesterol have been compared. In both crude and purified systems, the conversion of the monohydroxycholesterols is somewhat more rapid than that of cholesterol. However, the dihydroxycholesterol is a very much more efficient precursor of pregnenolone. Whereas small amounts of pregnenolone were formed from the four 20,22-epoxycholesteroIs, and slightly larger amounts from the two 20(22)-didehydrocholesterols in the crude enzyme systems, almost no conversion of these six compounds was observed with the purified system containing cytochrome P-45Oscc, adrenodoxin, adrenodoxin reductase, and an NADPH-generating system. It is concluded that the olefins and epoxides are not obligatory intermediates in the conversion of cholesterol to pregnenolone, and the conversions of cholesterol olefins and epoxides observed by us and by others may reflect the presence of extraneous enzymes such as double bond reductases and epoxide hydratases which are unrelated to pregnenolone biosynthesis. The relative effectiveness of the cholesterol olefins and epoxides, as well as 20-isocholesterol in inhibiting the formation of pregnenolone from [4-14C]cholesterol has been determined. The compounds which have the same configuration as cholesterol at C-20 are more potent inhibitors of this conversion than the olefins in which the C-21, C-20, C-22, C-23 carbon system is planar, or than those compounds which have the opposite configuration to cholesterol at C-20 (i.e. 20-isocholesterol, (20S,22S)-20,22-epoxycholesterol and (20S,22R)-20,22-epoxycholesterol). The enzyme appears to be more fastidious in its steric requirement at C-20 than at C-22. Since the olefins and epoxides are stereochemically rigidified around the C-20 to C-22 bond, these inhibitor studies suggest that the natural conformation of cholesterol on the side chain cleavage enzyme system is such that the side chain is fully extended and thus closely resembles the conformation of cholesterol in the crystal state. Abbreviations. The following abbreviations are used : cytochrome P-45OSCC, a highly purified bovine adrenal cortex mitochondrial cytochrome P-450 that cleaves the side chain of cholesterol to pregnenolone and is inactive in the 11 P-hydroxylation reaction; pregnenolone, 3a-hydroxypregn-5-en-20-one; cyanoketone, 2cc-cyEnzymes. Adrenodoxin reductase (EC 1.6.7.1); glucose-6-phosphate dehydrogenase (EC 1 .I. 1.49).

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Section: Formution Of Pregnenolone From Cholesterol and Various Didehcontrasting

confidence: 98%

mentioning

confidence: 99%

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confidence: 99%

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Biosynthesis of Pregnenolone from Cholesterol by Mitochondrial Enzymes of Bovine Adrenal Cortex. The Question of the Participation of the 20(22)-Olefins and 20,22-Epoxides of Cholesterol

et al. 1978

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“…A similar hydroxylation pathway (involving a dihydroxylated intermediate) is observed in the synthesis of adrenal steroids ((20R,22R)-dihydroxycholesterol). At this moment there is also no general agreement on the exact pathway in which the side-chain cleavage of cholesterol to pregnenolone takes place (Kraaipoel et al, 1975(Kraaipoel et al, , 1978.…”

Section: Introductionmentioning

confidence: 93%

Cerebrotendinous xanthomatosis: A review of biochemical findings of the patient population in the netherlands

Koopman

Wolthers

Molen

et al. 1987

J of Inher Metab Disea

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This study gives a review of the results obtained from biochemical investigations of 20 patients in The Netherlands suffering from cerebrotendinous xanthomatosis, an inborn error of metabolism in bile acid synthesis. Diagnosis can best be established by determining the excretion of urinary bile alcohols, in particular 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha,23,25-pentol, in urine by means of capillary gas chromatography. Measurement of serum cholestanol levels or serum cholestanol/cholesterol ratios, commonly used for establishing cerebrotendinous xanthomatosis, are not reliable. The effectiveness of the different therapies, i.e. administration of bile acids, can be evaluated by monitoring the urinary excretion of bile alcohols. From such investigations it was concluded that cholic acid especially, but also chenodeoxycholic acid are the therapies of choice for the treatment of cerebrotendinous xanthomatosis. All patients, until now diagnosed in The Netherlands were not discovered before the third or fourth decade of life because the characteristic signs only then become manifest clearly. Unfortunately, because sterol storage is almost irreversible, therapy only results in minor improvements of the patient's condition. Therefore early detection of the presence of cerebrotendinous xanthomatosis is desirable so that treatment can start before extensive storage of sterols is a fact. We developed some laboratory assays with the purpose of early detection. One consists of the detection of cerebrotendinous xanthomatosis carriers by subjecting them to oral cholestyramine administration and monitoring the urinary excretion of the bile alcohol 5 beta-cholestane-3 alpha,7 alpha,12 alpha,23,25-pentol before and after treatment. Secondly, a relatively simple screening test for cerebrotendinous xanthomatosis was developed based on an enzymatic assay of 7 alpha-hydroxylated steroids in urine. After suitable modification this assay in principle allows the screening of large populations for the existence of cerebrotendinous xanthomatosis and thus to detect the disease at an earlier stage of life.

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“…Systematic nomenclature for trivial names includes: [5,6]. In contrast Kraaipoel et al observed the incorporation of 0 from water into the glycol III during the biosynthesis of pregnenolone from cholesterol [7]. Such discrepancies have revived our interest in the metabolic role of the hydroperoxide-glycol conversion.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of cholesterol side‐chain cleavage: Enzymic rearrangement of 20β‐hydroperoxy‐20‐isocholesterol to 20β,21‐dihydroxy‐20‐isocholesterol

Lier

Rousseau

1976

FEBS Letters

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Incorporation of H₂¹⁸O into 20α, 22R‐di‐OH cholesterol: Evidence for an epoxide—diol pathway in the adrenocortical cholesterol side‐chain cleavage mechanism

Cited by 23 publications

References 14 publications

Biosynthesis of Pregnenolone from Cholesterol by Mitochondrial Enzymes of Bovine Adrenal Cortex. The Question of the Participation of the 20(22)-Olefins and 20,22-Epoxides of Cholesterol

Biosynthesis of Pregnenolone from Cholesterol by Mitochondrial Enzymes of Bovine Adrenal Cortex. The Question of the Participation of the 20(22)-Olefins and 20,22-Epoxides of Cholesterol

Cerebrotendinous xanthomatosis: A review of biochemical findings of the patient population in the netherlands

Mechanism of cholesterol side‐chain cleavage: Enzymic rearrangement of 20β‐hydroperoxy‐20‐isocholesterol to 20β,21‐dihydroxy‐20‐isocholesterol

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Incorporation of H218O into 20α, 22R‐di‐OH cholesterol: Evidence for an epoxide—diol pathway in the adrenocortical cholesterol side‐chain cleavage mechanism

Cited by 23 publications

References 14 publications

Biosynthesis of Pregnenolone from Cholesterol by Mitochondrial Enzymes of Bovine Adrenal Cortex. The Question of the Participation of the 20(22)-Olefins and 20,22-Epoxides of Cholesterol

Biosynthesis of Pregnenolone from Cholesterol by Mitochondrial Enzymes of Bovine Adrenal Cortex. The Question of the Participation of the 20(22)-Olefins and 20,22-Epoxides of Cholesterol

Cerebrotendinous xanthomatosis: A review of biochemical findings of the patient population in the netherlands

Mechanism of cholesterol side‐chain cleavage: Enzymic rearrangement of 20β‐hydroperoxy‐20‐isocholesterol to 20β,21‐dihydroxy‐20‐isocholesterol

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Incorporation of H₂¹⁸O into 20α, 22R‐di‐OH cholesterol: Evidence for an epoxide—diol pathway in the adrenocortical cholesterol side‐chain cleavage mechanism