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The conversion of cholest-7-en-3beta-ol into cholesterol. General comments on the mechanism of the introduction of double bonds in enzymic reactions.

ABSTRACT: Convenient syntheses of 6beta-tritiated Delta(7)-cholestenol and 3alpha-tritiated Delta(7)-cholestene-3beta,5alpha-diol are described. It was shown that the conversion of 6beta-tritiated Delta(7)-cholestenol into cholesterol is accompanied by the complete retention of label. It was unambiguously established that the overall reaction leading to the introduction of the double bond in the 5,6-position in cholesterol occurs via a cis-elimination involving the 5alpha- and 6alpha-hydrogen atoms and that during this process the 6beta-hydrogen atom remains completely undisturbed. Metabolic studies with 3alpha-tritiated Delta(7)-cholestene-3beta,5alpha-diol revealed that under anaerobic conditions the compound is not converted into cholesterol. This observation, coupled with the previous work of Slaytor & Bloch (1965), is interpreted to exclude a hydroxylation-dehydration mechanism for the origin of the 5,6-double bond in cholesterol. It was also shown that under aerobic conditions 3alpha-tritiated Delta(7)-cholestene-3beta,5alpha-diol is efficiently converted into cholesterol and that this conversion occurs through the intermediacy of 7-dehydrocholesterol. Cumulative experimental evidence presented in this paper and elsewhere is used to suggest that the 5,6-double bond in cholesterol originates through an oxygen-dependent dehydrogenation process and a hypothetical mechanism for this and related reactions is outlined.

SUBMITTER: Dewhurst SM

PROVIDER: S-EPMC1198440 | biostudies-other | 1967 Dec

REPOSITORIES: biostudies-other

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The conversion of cholest-5-en-3beta-ol into cholest-7-en-3beta-ol by the echinoderms Asterias rubens and Solaster papposus.

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| S-EPMC1165273 | biostudies-other

Mode of formulation of cholesta-5,7-dien-3beta-ol from Cholest-5-en-3beta-ol by Larvae of Calliphora erythrocephala.

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Project description:1. The syntheses of Delta(7)-[4-(14)C]cholestenol (XVI, Scheme 3) and Delta(7)-[6alpha-(3)H]-cholestenol (XII, Scheme 2) are described. 2. The metabolism of doubly labelled Delta(7)-cholestenol (II, Scheme 1) by rat-liver homogenates was studied. 3. During the enzymic conversion of Delta(7)-cholestenol into cholesterol (IV, Scheme 1) the 6alpha-hydrogen atom of the former is lost and the overall reaction corresponds to a cis-elimination. 4. In the light of these results various mechanisms for the conversion of Delta(7)-cholestenol into cholesterol are discussed.

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The biological conversion of 7-dehydrocholesterol into cholesterol and comments on the reduction of double bonds.

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| S-EPMC1198583 | biostudies-other

A novel olefinic rearrangement. The enzymic conversion of cholesta-7,9-dien-3 -ol into cholesta-8,14-dien-3 -ol.

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The isolation of cholest-5-ene-3beta,26-diol from human brain.

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