The essay examines the evidence upon which the presently accepted version of the mechanism of the cytochrome P450(scc)-catalyzed-cleavage of the sidechain of cholesterol is based. This analysis indicates that the generally held view of the process (two consecutive hydroxylations, followed by cleavage of the resulting glycol) most likely does not describe the true mechanism. The available evidence can not be used to support this traditional notion. Two alternative hypotheses are proposed.

Twenty monohydroxylated cholesterol derivatives have been characterized by high performance liquid column chromatography and by chemical ionization (CI) mass spectrometry. With ammonia as reagent gas four ions are formed: an ammonium adduct [M + NH 4 ] + , a substitution ion [M + NH 3 -OH] + and elimination ions [M-OH] + and [M-H 2 O-OH] + ]. Thermally stable stenediols exhibit [M + NH 4 ] + as principal ion, less stable allylic or tertiary alcohol derivatives the elimination ions [M-OH] + or [M-H 2 O-OH] + . With methane or isobutane as reagent gas monohydroxylated cholesterols yield five ions: the protonated molecular ion [M + H] + , molecular ion[M] + , hydride abstraction ion [M-H] + , and elimination ions [M-H 2 O + H] + and [M-2H 2 O + H] + , the principal ion uniformly being the [M-H 2 + H] + ion. Methane CI mass spectra of trimethylsilyl ether derivatives of the side-chain hydroxycholesterols exhibit unique fragmentation ions [C n H 2n OSi(CH 3 ) 3 ] + derived from α-cleavages diagnostic of the site of side-chain hydroxylation.

Human aorta, liver, and plasma have been examined for the presence of fatty acylesters of oxidized cholesterol derivatives using high performance liquid chromatography and chemical ionization mass spectrometry. Many such sterol esters have been detected, including eight individual diesters and six individual monoesters of six sterols and six C14-C18 fatty acids. Mono- and di-esters of the epimeric 5-cholestene-3β,7-diols, 5-cholestene-3β,25-diol, and a 5-cholestene-3β,26-diol were found at μ/g levels in aorta; palmitate esters of 5-cholestene-3β,25-diol and 3β-hydroxy-5-cholesten-7-one were detected at ng/g levels in liver; and esterified 5-cholestene-3β,7α-diol,5-cholestene-3β,7β-diol, 3β-hydroxy-5-choles ten-7-one, a 5-cholestene-3β.24-diol, 5-cholestene-3β,25-diol, and a 5-cholestene-3β,26-diol were present in plasma at ng/ml levels. The presence of esterified 5-cholestene-3β,7α-diol, 5-cholestene-3β,7β-diol, and 3β-hydroxy-5-cholesten-7-one together may be interpreted as evidence of in vivo lipid peroxidation of cholesterol.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHydroxyl ion negative chemical ionization mass spectra of steroidsT. A. Roy, F. H. Field, Yong Yeng. Lin, and Leland L. SmithCite this: Anal. Chem. 1979, 51, 2, 272–278Publication Date (Print):February 1, 1979Publication History Published online1 May 2002Published inissue 1 February 1979https://pubs.acs.org/doi/10.1021/ac50038a028https://doi.org/10.1021/ac50038a028research-articleACS PublicationsRequest reuse permissionsArticle Views77Altmetric-Citations36LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Cholest-5-ene-3β,24-diol (cerebrosterol) was identified as a minor sterol of rat brain. The sterol occurs at levels comparable to those of human and other mammalian brain and appears to accumulate during maturation. Immature rat brain had 12.5–13.8 μg/g fresh brain; adult rat brain had 27.5–34.4 μg/g. The sterol was detected in nuclear, mitochondrial, microsomal and soluble fractions but was greatest in myelin and nerve endings fractions. Rat brain homogenates and microsomal (105000 × g pellet) fractions therefrom transformed [1,2-3H]cholesterol to [3H]cholest-5-ene-3β-diol in 0.15–0.18% yields.

The sterol composition of the warm-water brown alga Sargassum fluitans Børgesen of the Gulf of Mexico was determined by TLC, GLC and IR measurements. The presence of over ten sterols was suggested, of which four (fucosterol, cholesterol, 24-methylenecholesterol, and trans - 22-dehydrocholesterol) were identified and four (a 24-methylcholesterol, a 24-ethylcholesterol, a 24-methyl- trans -22-dehydrocholestero 1 and a 24-ethyl- trans -22-dehydrocholesterol) were recognized but not definitively identified. Saringosterol and 24-ketocholesterol were not found. The crude sterol mixture from S. fluitans was oxidized by osmium tetroxide to 24-ketocholesterol in poor yield.

The sterol composition of the warm-water brown alga Sargassum fluitans Børgesen of the Gulf of Mexico was determined by TLC, GLC and IR measurements. The presence of over ten sterols was suggested, of which four (fucosterol, cholesterol, 24-methylenecholesterol, and trans- 22-dehydrocholesterol) were identified and four (a 24-methylcholesterol, a 24-ethylcholesterol, a 24-methyl-trans-22-dehydrocholestero 1 and a 24-ethyl-trans-22-dehydrocholesterol) were recognized but not definitively identified. Saringosterol and 24-ketocholesterol were not found. The crude sterol mixture from S. fluitans was oxidized by osmium tetroxide to 24-ketocholesterol in poor yield.

Aerobic incubations of rac-17β-hydroxyestra-4,8(14)-dien-3-one with Curvularia lunata NRRL 2380 gave rac-10β,17β-dihydroxyestra-4,8(14)-dien-3-one, rac-11β, 17β-dihydroxyestra-4,8(14)-dien-3-one, and rac-7α,17β-dihydroxyestra-4, 8(14)-dien-3-one. Some resolved 17β-hydroxyestra-4,8(14)-dien-3-one of natural configuration was also recovered. Structures of the hydroxylated products were determined from their spectral behavior. These results differ from our prior work where resolved hydroxylation products were obtained from rac-17β-hydroxyestr-4-en-3-one with C. lunata. These and other related points are discussed in speculation regarding microbial hydroxylase substrate specificity.

19-Nortestosterone induces hydroxylases for its own metabolism by Curvularia lunata NRRL 2380, optimum induction times of 1–3 h being indicated. Comparison of product spate and hydroxylation rates for vegetative cell culture incubations and for cell-free enzyme systems suggests that the vegetative cell system may be used for study of the initial kinetics of hydroxylation of steroid substrates without interference of endogenous cellular metabolism. Double reciprocal plots of kinetic data establish that the three major modes of transformation of 19-nortestosterone (to the 10β-, the 11β-, and the 14α-monohydroxylated derivatives) have identical apparent Michaelis constants (Km 0.34 mM). Mathematical treatment of a model system supports identical Km values as found experimentally. Arguments based on these kinetics are presented which suggest that the 19-norsteroid hydroxylase system of C. lunata NRRL 2380 not be three individual hydroxylases acting independently but rather be a single hydroxylase of more generalized function.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCorrection. The Synthesis of Methyl 13,16-Cycloatisan-18-oate (Methyl anti-trachylobanateW Herz, R Mirrington, H Young, and Y LinCite this: J. Org. Chem. 1969, 34, 11, 3715Publication Date (Print):November 1, 1969Publication History Published online10 September 2003Published inissue 1 November 1969https://pubs.acs.org/doi/10.1021/jo01263a616https://doi.org/10.1021/jo01263a616research-articleACS PublicationsRequest reuse permissionsArticle Views14Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts