The sterol compositions of six Cucurbitaceae seeds, Cucurbita pepo , C. lagenaria , Citrullus lanatus , Cucumis sativus , C. melo and Luffa aegyptiaca , were examined by TLC, GLC, HPLC and m some cases by mass spectrometry and 1 HNMR spectroscopy. Thirteen components were identified. They were codisterol, 25(27)-dehydroporiferasterol, clerosterol, isofucosterol, stigmasterol, campesterol, 22-dihydrobrassicasterol, sitosterol, 25(27)-dehydrofungisterol, 25(27)-dehydrochondrillasterol, 24β-ethyl-25(27)-dehydrolathosterol, avenasterol, spinasterol, 24ξ-methyllathosterol and 22-dihydrospinasterol. 24-Methylenecholesterol may also have been present. The Δ 5 -sterols were observed in all species. The pattern of sterols suggests the existence of four biosynthetic pathways operating from a 24(25)-dehydroprecursor. This work represents only the second time either codisterol or 25(27)-dehydrofungisterol has been isolated from a higher plant.

Saccharomyces cerevisiae is known to absorb sterols readily in the absence of air. As shown in this paper, yeast cells also will absorb sterols with and without various double bonds or an alkyl group at C-24 in the presence of air at a concentration (ca. 10% of the gas phase) which is growth-limiting due to limited sterol synthesis. However, if the growth conditions are changed to be fully aerobic, sterol is no longer absorbed to any significant extent even when the sterol in the medium (ergosterol) is the same as that present in the cells. This implies that sterol in the medium does not equilibrate passively with sterol in the plasma membrane and that some sort of facilitated transport, which can be turned on and off, is responsible for the entry of sterol when it occurs as a response to an inadequate endogenous supply of sterol. In agreement with facilitated transport mediated by protein binding, yeast cells in an auxotrophic state for sterol exhibit a high degree of stereoselectivity with respect to the orientation of the side chain around the C-17(20)-bond. For instance, E-17(20)- but not Z-17(20)-dehydrocholesterol is absorbed by cells undergoing limited growth with 10% air.

When accumulation of squalene was used as a measure of the flow of carbon into the sterol pathway in whole cells of semi-anaerobic Saccharomyces cerevisiae, both ergosterol and cholesterol were found to be inhibitory. However, at equivalent concentrations in the medium ergosterol was substantially the more potent inhibitor. Marked differences found in the absorption and esterification of the two sterols failed to account for the observed difference in their capacities to act as feedback agents. Cholesterol was much more effectively absorbed as well as esterified, but, when the abilities of the two sterols to lower the squalene level were calculated on the basis of free sterol in the cells, ergosterol remained more effective by a factor of four.

While seeds ofCucurbita maxima contain both Δ5- and Δ7-sterols, the former, which have been described earlier, now have been found to disappear during germination. This suggests that a function exists for the Δ5-compounds only in the early part of the life cycle ofC. maxima, unlike most of the other higher plants studied. In contrast to the Δ5-sterols, the level of Δ7-sterols increased during germination as well as during seedling development and maturation. The period of transition between germination and seedling development appeared to be of special importance in terms of sterol changes. This period represented a surge of sterol biosynthesis with an ontogenetic shift in sterol composition from approximately equal amounts of 24α- and 24β-ethyl stereochemistry to a predominance of the former. The sterol composition of the mature plants included only about 5% of the 24β-ethylsterols. The configurational relationships were demonstrated by high resolution1H-NMR. The sterols of the mature plants were: 25(27)-dehydrochondrillasterol, 24β-ethyl-25(27)-dehydrolathosterol, avenasterol, spinasterol, 22-dihydrospinasterol and 24ξ-methyllathosterol. Based on the changes which occurred in the relative amounts of the Δ7-sterols, it did not appear that the Δ5-components were being converted to their Δ7-analogs.

A series of 20(R)-n-alkylpregn-5-en-3β-ols with 0 to 9 (but not with 12) C-atoms in the alkyl group induced formation of oogonia inPhytophthora cactorum. However, maturation of the oogonia into germinating oospores occurred only when the alkyl group had 4–7 C-atoms.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXT13C Nmr of TetrahymanolMabry Benson, W. David Nes, William R. Nes, and J. R. LandreyCite this: J. Nat. Prod. 1983, 46, 2, 274–276Publication Date (Print):March 1, 1983Publication History Published online1 July 2004Published inissue 1 March 1983https://pubs.acs.org/doi/10.1021/np50026a024https://doi.org/10.1021/np50026a024research-articleACS PublicationsRequest reuse permissionsArticle Views91Altmetric-Citations9LEARN 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

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXT13C Nmr of TetrahymanolMabry Benson, W. David Nes, William R. Nes, and J. R. LandreyCite this: J. Nat. Prod. 1983, 46, 2, 274–276Publication Date (Print):March 1, 1983Publication History Published online1 July 2004Published inissue 1 March 1983https://doi.org/10.1021/np50026a024RIGHTS & PERMISSIONSArticle Views88Altmetric-Citations9LEARN 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 InReddit PDF (184 KB) Get e-Alerts Get e-Alerts

The Δ5-sterol, androst-5-en-3β-ol, which has no side chain at C-17, did not permit molting of the insectHeliothis zea, growth of either the protozoanTetrahymena pyriformis, or the yeastSaccharomyces cerevisiae adapted to anaerobic conditions, nor was the sterol esterified by a mammalian microsomal ACAT preparation. However, the sterol did form a liposome with egg lecithin and, when fed to mice, did inhibit hepatic cholesterol synthesis. 21-Isopentylcholesterol also formed a liposome but neither supported the growth of the yeast nor was metabolized by the protozoan. When sterols, 20(R)-n-alkylpregn-5-en-3β-ols, with side chains of varying lengths were added to the medium of the protozoan, maximal esterification with fatty acids occurred with the 20(R)-n-pentyl derivative, and maximal inhibition of tetrahymanol formation occurred with then-butyl,n-pentyl andn-hexyl derivatives. In all of the assays, cholesterol showed a positive response, either permitting molting or growth, being metabolized, inhibiting sterol or tetrahymanol synthesis, or forming a liposome.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTProof of Structure For 24β-Methylcholesterol in the Alga Coccomyxa elongata by 1H- and 13C-nmr and Mass SpectroscopyWilliam R. Nes and John E. ZaremboCite this: J. Nat. Prod. 1981, 44, 1, 7–13Publication Date (Print):February 1, 1981Publication History Published online1 July 2004Published inissue 1 February 1981https://pubs.acs.org/doi/10.1021/np50013a002https://doi.org/10.1021/np50013a002research-articleACS PublicationsRequest reuse permissionsArticle Views79Altmetric-Citations2LEARN 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

Purified flagella of the eukaryotic algaChlamydomonas reinhardi have a sterol composition (55% ergosterol [24β-methylcholesta-5,7,22-trans-trien-3β-ol] and 45% 7-dehydroporiferasterol [24β-ethylcholesta-5,7,22-trans-trien-3β-ol]) identical of that of the whole algal cell. Fatty acids isolated fromC. reinhardi flagella were identified as 16∶0, 18∶0, 18∶1, 18∶2 and 18∶3. Whole cell fatty acids included 14∶0, 16∶2 and 16∶3 in addition to those found in the flagella. Triunsaturates comprised 22.9% of the flagellar fatty acids and 76.4% of those from the whole cell.

Anaerobically grown Saccharomyces cerevisiae retained the ability to transfer a C1-group to the C-24 position of a delta 24(25)-sterol and to reduce the delta 25(28)-bond of a 24-methylenesterol. Both desmosterol and 24-methylenecholesterol yielded 24 beta-methylcholesterol. However, when the substituent at C-24 was enlarged to a 24-ethylidene group (fucosterol), reduction of the delta 24(28)-bond did not occur. In no cases was a delta 7- or a delta 22-bond introduced. Because the delta 24(28)-bond was reduced in the absence of the delta 22-bond, the delta 22-bond is not an obligatory requirement for reduction.

Cultures of Tetrahymena pyriformis were incubated with various sterols and the extent of dehydrogenation at C-7 and C-22 was determined. The sterols incubated were desmosterol, 22-dehydrodesmosterol, 24-methyldesmosterol, 24 alpha-methylcholesterol (campesterol), 24-methylene-cholesterol, isohalosterol (26,27-bisnorcampesterol, also known as 24,24-dimethylchol-5-en-e beta-ol, a naturally occurring C26-sterol), and 20-isohalosterol. 20-Isohalosterol was not metabolized, while products with delta 7- and delta 22-bonds were formed from isohalosterol and all of the other sterols studied. This confirms an earlier conclusion, based on results with 20-isocholesterol and cholesterol, that inversion of the configuration from 20(R) to 20(S) completely prevents metabolism both in the nucleus and the side chain. On the other hand, changes in the electronics or stereochemistry at C-24 had a direct affect only on metabolism in the side chain. The presence of a methyl group at C-24 reduced the yield of metabolites with a delta 22-bond relative to those with a delta 7-bond producing an accumulation of 7-dehydro metabolite. A double bond at position-24 counteracted this steric effect, presumably by enhancing the rate of dehydrogenation, and a delta 24(28)-bond was more effect than was a delta 24(25)-bond.

Sterols were present in neither of two representative species of photosynthetic bacteria, Rhodopseudomonas spheroides and Chromatium vinosum . These organisms were grown under conditions commonly viewed as anaerobic. However, such conditions did not prevent Saccharomyces cerevisiae from biosynthesizing sterols, although they did induce accumulation of both 4,4-dimethyl and 4-desmethyl intermediates. Since the photosynthetic organisms did not biosynthesize sterols, bacterial photosynthesis must not be mated genetically or functionally to sterol biosynthesis. In contrast to what the literature records, Escherichia coli , grown under fully aerobic conditions, also failed to contain sterols which indicates that bacterial aerobiosis does not necessarily imply either the presence of sterol biosynthesis or a requirement for an exogenous source of sterols. Among the lipids of E. coli was a substance with the formula C 16 H 32 O 2 which moved in silica gel TLC at a rate similar to that of sterols and may have been a keto-alcohol of the same formula already isolated from coliforms. In the photosynthetic bacteria the major neutral lipid after saponification was phytol, in agreement with expectation based on the presence of bacteriochlorophyll-a.