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The stereochemistry of hydrogen elimination from C-7 in cholesterol and ergosterol biosynthesis.

ABSTRACT: The synthesis of [7alpha-(3)H]lanosterol is described. It is shown that in the conversion of [7alpha-(3)H,26,27-(14)C(2)]lanosterol into cholesterol by a rat liver system, it is the 7beta-hydrogen atom that is predominantly removed. On the other hand, the conversion of doubly labelled lanosterol into ergosterol by whole yeast cells results in the loss of the 7alpha-hydrogen atom. These results therefore suggest that the C-7 hydrogen atoms with opposite stereochemistry are labilized by the rat liver and the yeast Delta(8)-Delta(7) steroid isomerases.

SUBMITTER: Akhtar M

PROVIDER: S-EPMC1178958 | biostudies-other | 1970 Apr

REPOSITORIES: biostudies-other

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The stereochemistry of hydrogen elimination from C-7 during biosynthesis of ecdysones in insects and plants.

Project description:1. [7alpha-(3)H(1)]- and [7beta-(3)H(1)]-Cholesterol were synthesized by a modified method. 2. The stereochemistry of Delta(7)-bond formation during ecdysone and ecdysterone biosynthesis in the insect, Calliphora erythrocephala and the plants, Taxus baccata and Polypodium vulgare was investigated by using [4-(14)C,7alpha-(3)H(1)]cholesterol and [4-(14)C,7beta-(3)H(1)]cholesterol. 3. In each case, the 7beta hydrogen was stereospecifically eliminated. 4. The possible significance of the results is discussed in relation to double-bond formation in other systems and the stage at which the Delta(7) bond is introduced during ecdysone biosynthesis.

| S-EPMC1165933 | biostudies-other

The stereochemistry of the hydrogen elimination in the biological conversion of cholest-7-en-3-beta-ol into cholesterol.

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.

| S-EPMC1270267 | biostudies-other

Carotenoid biosynthesis in a Flavobacterium sp.: stereochemistry of hydrogen elimination in the desaturation of phytoene to lycopene, rubixanthin and zeaxanthin.

Project description:[2-(14)C,(2R)-2-(3)H(1)]- and [2-(14)C,(2S)-2-(3)H(1)]-Mevalonates were rapidly incorporated into phytoene, lycopene, rubixanthin and zeaxanthin in a Flavobacterium system obtained by disruption of the bacterial cells by shaking with glass beads. Four hydrogen atoms arising from the 2-pro-S-hydrogen atoms of mevalonate were lost in the desaturation of phytoene to lycopene, rubixanthin and zeaxanthin. The desaturation of phytoene involves trans-elimination of hydrogen in the introduction of the double bonds at C-7, C-11, C-7' and C-11'.

| S-EPMC1177920 | biostudies-other

The stereochemistry of hexahydroprenol, ubiquinone and ergosterol biosynthesis in the mycelium of Aspergillus fumigatus Fresenius.

Project description:1. The mycelium of Aspergillus fumigatus has been shown to incorporate mevalonate into squalene, ubiquinone, ergosterol and hexahydroprenol. 2. The (3)H/(14)C ratio in ubiquinone, biosynthesized from [2-(14)C-(4R)-4-(3)H(1)]mevalonate, is the same as in the squalene; essentially no (3)H was incorporated from [2-(14)C-(4S)-4-(3)H(1)]mevalonate, indicating the biosynthesis of biogenetically trans-isoprene units. 3. The (3)H/(14)C ratio for ergosterol (from ;4R-mevalonate') was 3:5, showing that the proton at C-24 is not lost during alkylation of the side chain; it probably migrates to C-25. 4. As (3)H from both mevalonates was incorporated into the hexahydroprenols the biosynthesis of both cis- and trans-isoprene units must occur. 5. The saturated omega- and psi-isoprene units are shown to be biogenetically trans, as are two of the unsaturated residues. 6. The saturated alpha- and unsaturated beta-isoprene residues are both biogenetically cis. 7. An inexplicable loss of approximately half of the olefinic protons from the cis-portion of hexahydroprenol occurs; possible reasons for this loss are discussed. 8. Increase in chain length of the hexahydroprenols is by a cis addition. 9. A biosynthesis of hexahydroprenols by addition of cis-isoprene units to all-trans-geranylgeranyl pyrophosphate, or a dihydro or tetrahydro derivative thereof, is suggested.

| S-EPMC1270544 | biostudies-other

The stereochemistry of hydrogen elimination during 7,8-double bond formation by Tetrahymena pyriformis.

Project description:It is shown that formation of the 7,8-double bond in the conversion of cholesterol into cholesta-5,7,22-trien-3beta-ol involves the removal of the 7beta- and 8beta-hydrogen atoms.

| S-EPMC1185370 | biostudies-other

The stereochemistry of hydrogen transfer from reduced nicotinamide-adenine dinucleotide phosphate in the reduction of ethylenic linkages during cholesterol biosynthesis.

Project description:It is shown that during the saturation of steroid carbon-carbon double bonds at Delta(24,25) and Delta(14,15) the ;hydride ion' originates from the 4B side of the NADPH.

| S-EPMC1179453 | biostudies-other

The transfer of hydrogen from C-24 to C-25 in ergosterol biosynthesis.

Project description:1. A convenient synthesis of 3-hydroxytrisnorlanost-8-en-24-al and its conversion into [24-(3)H]lanosterol and [26,27-(14)C(2)]lanosterol is described. 2. A method for the efficient incorporation of lanosterol into ergosterol by the whole cells of Saccharomyces cerevisiae is also described. 3. It is shown that in the biosynthesis of ergosterol from doubly labelled lanosterol the C-24 hydrogen atom of lanosterol is retained in ergosterol. 4. On the basis of unambiguous degradations it is shown that the C-alkylation step in ergosterol biosynthesis is accompanied by the migration of a hydrogen atom from C-24 to C-25. 5. The mechanism for the biosynthesis of the ergosterol side chain is presented. 6. Mechanisms of other C-alkylation reactions are also discussed.

| S-EPMC1270458 | biostudies-other

Characterization of the Ergosterol Biosynthesis Pathway in Ceratocystidaceae.

Project description:Terpenes represent the biggest group of natural compounds on earth. This large class of organic hydrocarbons is distributed among all cellular organisms, including fungi. The different classes of terpenes produced by fungi are mono, sesqui, di- and triterpenes, although triterpene ergosterol is the main sterol identified in cell membranes of these organisms. The availability of genomic data from members in the Ceratocystidaceae enabled the detection and characterization of the genes encoding the enzymes in the mevalonate and ergosterol biosynthetic pathways. Using a bioinformatics approach, fungal orthologs of sterol biosynthesis genes in nine different species of the Ceratocystidaceae were identified. Ergosterol and some of the intermediates in the pathway were also detected in seven species (Ceratocystis manginecans, C. adiposa, Huntiella moniliformis, Thielaviopsis punctulata, Bretziella fagacearum, Endoconidiophora polonica and Davidsoniella virescens), using gas chromatography-mass spectrometry analysis. The average ergosterol content differed among different genera of Ceratocystidaceae. We also identified all possible terpene related genes and possible biosynthetic clusters in the genomes used in this study. We found a highly conserved terpene biosynthesis gene cluster containing some genes encoding ergosterol biosynthesis enzymes in the analysed genomes. An additional possible terpene gene cluster was also identified in all of the Ceratocystidaceae. We also evaluated the sensitivity of the Ceratocystidaceae to a triazole fungicide that inhibits ergosterol synthesis. The results showed that different members of this family behave differently when exposed to different concentrations of triazole tebuconazole.

| S-EPMC8004197 | biostudies-literature

The stereochemistry of betulaprenol biosynthesis.

Project description:By using stereospecifically double-labelled radioactive mevalonates it was shown that betulaprenols-6 to -9, found in the woody tissue of Betula verrucosa, each contain three biogenetically trans-isoprene residues and that the remaining residues are biogenetically cis. The results obtained with these radioactive mevalonates also indicated that the activity of isopentenyl pyrophosphate isomerase is low relative to the activity of prenyltransferase in this woody tissue. The incorporation of radioactive farnesyl pyrophosphate and radioactive geranylnerol and the lack of incorporation of radioactive geranylgeraniol into betulaprenols-6 to -9 demonstrated that they are formed by the cis-additions of isoprene residues to all-trans-farnesyl pyrophosphate.

| S-EPMC1178863 | biostudies-other

Comparative Study of the Condensing Effects of Ergosterol and Cholesterol.

Project description:Cholesterol, due to its condensing effect, is considered an important regulator of membrane thickness. Other sterols, due to their structural similarities to cholesterol, are often assumed to have a universal effect on membrane properties similar to the condensing effect of cholesterol, albeit possibly to different degrees. We used x-ray diffraction to investigate this assumption. By the combination of lamellar diffraction and grazing-angle scattering, we measured the membrane thickness and the tilt-angle distribution of the lipid's hydrocarbon chains. This method is sensitive to phase separation, which is important for examining the miscibility of sterols and phospholipids. Mixtures of ergosterol or cholesterol with dimyristoylphosphatidylcholine, palmitoyloleoylphosphatidylcholine, and dioleoylphosphatidylcholine were systematically studied. We found that mixing ergosterol with phospholipids into a single phase became increasingly difficult with higher sterol concentrations and also with higher concentrations of unsaturated lipid chains. The only condensing effect of ergosterol was found in dimyristoylphosphatidylcholine, although the effect was less than one-third of the effect of cholesterol. Unlike cholesterol, ergosterol could not maintain a fixed electron density profile of the surrounding lipids independent of hydration. In dioleoylphosphatidylcholine and palmitoyloleoylphosphatidylcholine, ergosterol made the membranes thinner, opposite to the effect of cholesterol. In all cases, the tilt-angle variation of the chain diffraction was consistent with the membrane thickness changes measured by lamellar diffraction, i.e., a thickening was always associated with a reduction of chain tilt angles. Our findings do not support the notion that different sterols have a universal behavior that differs only in degree.

| S-EPMC4939751 | biostudies-literature

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