Sur le sterol a 26 atomes de carbone de l'algue rouge Rhodymenia palmata

Triterpene alcohols and sterols of the red alga Rhodymenia palmata have been investigated. Cycloartanol, 31-nor-cycloartanol and the C₂₆ sterol 24-dimethylchola-5,22-diene-3β-ol (1) have been identified. Feeding experiments have been performed using 1-¹⁴C-acetate, 5-¹⁴C-mevalonic acid or ¹⁴C-methylmethionine. The C₂₇, C₂₈ and C₂₉ sterols incorporate radioactivities but the C₂₆ sterol is unlabelled after each experiment; its possible origin is discussed.     

Sterols from some black sea ulvaceae

The free and esterified sterol composition of Ulva rigida and Enteromorpha linza (Ulvaceae) from the Black Sea was investigated. The main sterol component of Ulva rigida was identified as fucosterol. The influence of the season and water pollution on the sterol composition was investigated. The origin of the C₂₆,- and C₂₅-sterols and of saringasterol in these seaweeds is discussed.     

Sterols from some sponges

The sterol composition of four sponges was determined by a combination of gas chromatography and mass spectrometry. Cliona viridis and Chondrosia reniformis contained mainly C₂₇-C₂₉Δ⁵ mono- and di-unsaturated sterols. Halichondria bowerbanki and Hymeniacidon sanguinea contained stanols and Δ⁵-sterols. Cholestanol was the major component of the sterol mixtures.     

Hydrocarbons,sterols and tocopherols in the seeds of six Adansonia species

The composition of the unsaponifiable matter of the lipids of six Adansonia species (A. grandidieri, A. za, A. fony, A. madagascariensis, A. digitata and A. suarezensis) was investigated. The total unsaponifiable content, its general composition and the identity of the components of the hydrocarbon, sterol and tocopherol fractions are presented. The unsaponifiable content in oil ranges from 0.4 to 1.1% (hexane method) and from 0.6 to 2.2% (diethyl ether method). In two species (A. grandidieri and A. suarezensis) the major components are 4-demethylsterols (23–42%) tocopherols (37-10%) and hydrocarbons (15–17%). In both species examined, eight 4-demethylsterols occur in the sterol fraction with sitosterol (81–88%) being predominant. Among the four tocopherols present, γ-tocopherol (68–98%) is the major compound. Each Adansonia species shows a characteristic gas liquid chromatography pattern for the hydrocarbon fraction. Squalene is the major component for five species (40–75%). Iso-, anteiso- and other branched hydrocarbons were not identified but were present in small amounts in comparison with n-alkanes. The dominance of odd- over even-carbon number chain length of n-alkanes was not observed in any species. The results show that C₂₂, C₂₅, C₂₆, C₂₇, C₂₈ and C₂₉ are the most frequent major constituents.     

Dehydrodinosterol,dinosterone and related sterols of a non-photosynthetic dinoflagellate, Crypthecodinium cohnii

The heterotrophic dinoflagellate Crypthecodinium cohnii contained the 4α-methyl sterols, dinosterol, dehydrodinosterol (4α,23,24-trimethylcholesta-5,22-dien-3β-ol) and the tentatively identified 4α,24-dimethyl-cholestan-3β-ol and 4α,24-dimethylcholest-5-en-3β-ol. The major 4-demethyl sterol was cholesta-5,7-dien-3β-ol which was accompanied by a smaller amount of cholesterol and traces of several other C₂₇,C₂₈ and C₂₉ sterols. In addition, a 3-oxo-steroid fraction was isolated and the major component identified as dinosterone (4α,23,24-trimethylcholest-22-en-3-one). The possible biosynthetic relationships of these compounds are discussed.     

Sterols of the unicellular algae Nematochrysopsis roscoffensis and Chrysotila lamellosa: isolation of (24E)-24-n-propylidenecholesterol and 24-n-propylcholesterol

Two rare C₃₀-sterols, (24E)-24-n-propylidenecholest-5-en-3β-ol and 24-n-propylcholest-5-en-3β-ol, and (24S)-24-ethylcholesta-5,22-dien- 3β-ol (stigmasterol) are the major sterols of Nematochrysopsis roscoffensis, a Chrysophyte of the Sarcinochrysidales order. This unique sterol composition is different from the sterol contents of other Chrysophytes and justifies the peculiar position of the Sarcinochrysidales, which are by some characteristics morphologically and biologically related to the Phaeophyceae. The presence of (24S)-24-methylcholesta-5,22-dien-3β-ol (24-epibrassicasterol) as a major sterol in Chrysotila lamellosa is in accordance with the few previous results obtained from other Prymnesiophyceae, although the presence of the other major sterol, (24R)-24-ethylcholesta-5,22-dien-3β-ol (poriferasterol) has never been reported in these algae.     

24β-ethylsterols,n-alkanes and n-alkanols of Clerodendrum splendens

The sterols of Clerodendrum splendens, an angiosperm belonging to the family Verbenaceae, were found to possess a 24β-ethyl group. No other sterols were detected. The major sterol was 24β-ethylcholesta-5,22E,25(27)-trien-3β-ol [also known as 25(27)-dehydroporiferasterol]. A very small amount of what may have been its 22-dihydroderivative, clerosterol [also known as 25(27)-dehydroclionasterol] was also found. The dominant n-alkane was C₂₉ (n-nonacosane) and the dominant n-alkanol was C₂₈ (n-octacosanol).     

Sterol profiles of red algae

Twelve species of red algae belonging to the Orders Gelidiales, Cryptonemiales and Gigartinales were examined for sterols. Four species contained cholestan-3β-ol as the major sterol, accompanied by C₂₆, C₂₈ and C₂₉ stanols. Sterols not previously reported in algae were 24-dimethyl-5α-chol-22-en-3β-ol, cholest-22-en-3β-ol, cholest-7-en-3β-ol, 24ξ-methylcholest-22-en-3β-ol, 24-methylenecholestan-3β-ol, 24ξ-ethylcholestan-3β-ol and isofucostanol.     

The fatty acid and sterol composition of two marine dinoflagellates

The fatty acid, sterol and chlorophyll pigment compositions of the marine dinoflagellates Gymnodinium wilczeki and Prorocentrum cordatum are reported. The fatty acids of both algae show a typical dinoflagellate distribution pattern with a predominance of C₁₈, C₂₀ and C₂₂ unsaturated components. The acid 18:5ω3 is present at high concentration in these two dinoflagellates. G. wilczeki contains a high proportion (93.4%) of 4-methyl-5α-stanols including 4,23,24-trimethyl-5α-cholest-22E-en-3β-ol (dinosterol), dinostanol and 4,23,24-trimethyl-5α-cholest-7-en-3β-ol reported for the first time in dinoflagellates. The role of this sterol in the biosynthesis of 5α-stanols in dinoflagellates is discussed. P. cordatum contains high concentrations of a number of δ ²⁴⁽²⁸⁾-sterols with dinosterol, 24-methylcholesta-5,24(28)-dien-3β-ol, 23,24-dimethylcholesta-5,22E-dien-3β-ol, 4,24-dimethyl-5α-cholest-24(28)-en-3β-ol and a sterol identified as either 4,23,24-trimethyl- or 4-methyl-24-ethyl-5α-cholest-24(28)-en-3β-ol present as the five major components. The role of marine dinoflagellates in the input of both 4-methyl- and 4-desmethyl-5α-stanols to marine sediments is discussed.     

STEROLS OF 14 SPECIES OF MARINE DIATOMS (BACILLARIOPHYTA)1

The sterol compositions of 14 species of marine diatoms were determined by gas chromatography and gas chromatography-mass spectrometry. A variety of sterol profiles were found. The sterols 24-methylcholesta-5,22E-dien-3β-ol, cholest-5-en-3β-ol, and 24-methylcholesta-5,24(28)-dien-3β-ol, previously described as the most common sterols found in diatoms, were major sterols in only a few of the species. In light of this and other recent data, it is clear that these three sterols are not typical constituents of many diatom species. Most of the centric species examined had 24-methylcholesta-5,24(28)-dien-3β-ol and 24-methylcholest-5-en-3β-ol as two of their major sterols. The exception was Rhizosolenia setigera, which possessed cholesta-5,24-dien-3β-ol as its single major sterol. In contrast to the centric species, the pennate diatoms examined did not have any particular sterols common to most species. Minor levels ofΔ⁷-sterols, rarely found in large amounts in diatoms, were found in four species. C₂₉sterols were found in many species; seven contained 24-ethylcholest-5-en-3β-ol and three contained 24-ethylcholesta-5,22E-dien-3β-ol, reinforcing previous suggestions that C₂₉ sterols are not restricted to higher plants and macroalgae. 24-Ethylcholesta-5,22E-dien-3β-ol may prove to be useful for taxonomy of the genus Amphora and the order Thalassiophysales. A major sterol of Fragilaria pinnata was the uncommon algal sterol 23,24-dimethylcholesta-5,22E-dien-3β-ol. Cholesta-5,24-dien-3β-ol was the only sterol found in the culture of Nitzschia closterium. This differed from previous reports of 24-methylcholesta-5,22E-dien-3β-ol as the single major sterol in N. closterium. Two C₂₈ sterols possessing an unusual side chain were found in Thalassi-onema nitzschioides, a C_28:2 sterol (16%) and a C_28:1 sterol in lower abundance (2.5%), which may be 23-methylcholesta-5,22E-dien-3β-ol and 23-methyl-5α-cholest-22E-en-3β-ol, respectively. The species Cylindrotheca fusiformis, T. nitzschioides, and Skeletonema sp. may be useful as direct sources of cholesterol in mariculture feeds due to their moderate to high content of this sterol.     

Sterols of Saccharomyces cerevisiae erg6 Knockout Mutant Expressing the Pneumocystis carinii S‐Adenosylmethionine:Sterol C‐24 Methyltransferase

The AIDS‐associated lung pathogen Pneumocystis is classified as a fungus although Pneumocystis has several distinct features such as the absence of ergosterol, the major sterol of most fungi. The Pneumocystis carinii S‐adenosylmethionine:sterol C24‐methyltransferase (SAM:SMT) enzyme, coded by the erg6 gene, transfers either one or two methyl groups to the C‐24 position of the sterol side chain producing both C₂₈ and C₂₉ 24‐alkylsterols in approximately the same proportions, whereas most fungal SAM:SMT transfer only one methyl group to the side chain. The sterol compositions of wild‐type Sacchromyces cerevisiae, the erg6 knockout mutant (Δerg6), and Δerg6 expressing the P. carinii or the S. cerevisiae erg6 gene were analyzed by a variety of chromatographic and spectroscopic procedures to examine functional complementation in the yeast expression system. Detailed sterol analyses were obtained using high performance liquid chromatography and proton nuclear magnetic resonance spectroscopy (¹H‐NMR). The P. carinii SAM:SMT in the Δerg6 restored its ability to produce the C₂₈ sterol ergosterol as the major sterol, and also resulted in low levels of C₂₉ sterols. This indicates that while the P. carinii SAM:SMT in the yeast Δerg6 cells was able to transfer a second methyl group to the side chain, the action of Δ²⁴⁽²⁸⁾‐sterol reductase (coded by the erg4 gene) in the yeast cells prevented the formation and accumulation of as many C₂₉ sterols as that found in P. carinii.     

STEROLS OF PORPHYRIDIUM(RHODOPHYTA)1,2

Species of the unicellular Porphyridium have been examined for their sterol content. Clones of 4 species maintained in axenic, chemically-defined culture were analyzed—these included P. sordidum Geitler, P. purpureum (Bory) Ross, P. aerugineum Geitler and P. violaceum Kormnann(P. griseum Geitler was not available to use for examination). The major sterol was 22-dehydrocholesterol in all except P. aerugineum in which there was a mixture of this sterol, cholesterol and higher sterols. Traces of C₂₈ and C₂₉ sterols were detected in most instances as well.     

Functional importance for developmental regulation of sterol biosynthesis in Acanthamoeba castellanii

The sterol metabolome of Acanthamoeba castellanii (Ac) yielded 25 sterols. Substrate screening of cloned AcCYP51 revealed obtusifoliol as the natural substrate which converts to ?^8,14-sterol (<95%). The combination of [²H₃-methyl]methionine incubation to intact cultures showing C₂₈-ergosterol incorporates 2-²H atoms and C₂₉-7-dehydroporiferasterol incorporates 5 ²H-atoms, the natural distribution of sterols, CYP51 and previously published sterol methyltransferase (SMT) data indicate separate ?²⁴⁽²⁸⁾- and ?²⁵⁽²⁷⁾-olefin pathways to C₂₈- and C₂₉-sterol products from the protosterol cycloartenol. In cell-based culture, we observed a marked change in sterol compositions during the growth and encystment phases monitored microscopically and by trypan blue staining; trophozoites possess C₂₈/C₂₉-?^5,7-sterols, viable encysted cells (mature cyst) possess mostly C₂₉-?⁵-sterol and non-viable encysted cells possess C₂₈/C₂₉-?^5,7-sterols that turnover variably from stress to 6-methyl aromatic sterols associated with changed membrane fluidity affording lysis. An incompatible fit of steroidal aromatics in membranes was confirmed using the yeast sterol auxotroph GL7. Only viable cysts, including those treated with inhibitor, can excyst into trophozoites. 25-Azacycloartanol or voriconazole that target SMT and CYP51, respectively, are potent enzyme inhibitors in the nanomolar range against the cloned enzymes and amoeba cells. At minimum amoebicidal concentration of inhibitor amoeboid cells rapidly convert to encysted cells unable to excyst. The correlation between stage-specific sterol compositions and the physiological effects of ergosterol biosynthesis inhibitors suggests that amoeba fitness is controlled mainly by developmentally-regulated changes in the phytosterol B-ring; paired interference in the ?^5,7-sterol biosynthesis (to ?^5,7) - metabolism (to ?⁵ or 6-methyl aromatic) congruence during cell proliferation and encystment could be a source of therapeutic intervention for Acanthamoeba infections.     

Partial purification and specificity of triacylglycerol: Sterol acyltransferase from Sinapis alba

Triacylglycerol: sterol acyltransferase is present in roots of Sinapis alba seedlings. The enzyme is located predominantly in the cell membrane structures sedimenting at 300–16 000 g but can be solubilized by acetone treatment and buffer extraction. During gel filtration on Sephadex G-100 the acyltransferase activity was separated into two peaks corresponding to MW 1.8 × 10¹⁴ and MW ? 10⁵, respectively. A number of natural 3β-hydroxysterols can be esterified by the solubilized acyltransferase. The rate of esterification is much higher for sterols containing a planar ring system. The number and position of double bonds, as well as the structure of the side chain at C- 17 of the sterol molecule, are of secondary importance. Triacylglycerols containing fatty acids C, C₆-C₂₂ can be utilized as acyl donors. Among triacylglycerols containing saturated fatty acids, tripalmitoylglycerol (C_16:0) is the best acyl donor. For triacylglycerols containing C₁₈-fatty acids the following sequence was observed: trioleoylglycerol (C_18:1) > trilinoleoylglycerol (C_18:2) > trilinolenoylglycerol (C_18:3) > tristearoylglycerol (C_18:0).     

Les sterols de l'Ascomycete Leptosphaeria typhae

A mixture of C₂₈ and C₂₉ sterols have been isolated from Leptosphaeria typhae grown in vitro on “oat water” and characterized by GLC and MS. Mono-, di- and tri-unsaturated sterols are present in the extracts of fungi cultivated both in the dark and in the light but the sterol composition is different. The influence of “oat water” on sterol structure has been determined by comparison with the sterols of the same fungus grown on synthetic medium in the dark.     

Sterols of Xanthoria parietina: Evidence for two sterol ‘pools’ and the identification of a novel C,8 triene,ergosta-5,8,22-trien-3β-ol

Sterols extracted from Xanthoria parietina with organic solvents and released by saponification of the residual lichen tissue were analysed by GC-MS. The main components of the solvent-extractable sterols were two C₂₈ trienes and those of the more tightly bound sterols were ergost-5-en-3β-ol and two C₂₉ compounds. The structures of the C₂₈ compounds were shown to be ergosta-5,7,22-trien-3β-ol, Ia (ergosterol) and the previously unreported ergosta-5,8,22-trien-3β-ol, IIa, for which the name lichesterol is proposed. The main C₂₉ sterol was identified as (24R)-24-ethylcholesta-5,22-dien-3β-ol (poriferasterol).     

Sterol and other constituents of the brown alga Desmarestia aculeata

The brown alga Desmarestia aculeata was found to contain β-carotene, plastoquinone-9, fucoxanthin and a C₂₇ sterol with a novel side chain.     

The independence of photosynthesis and aerobiosis from sterol biosynthesis in bacteria

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 C₁₆H₃₂O₂ 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.     

Sterols of the mycobiont and phycobiont isolated from the litchen Xanthoria parietina

The mycobiont, Xanthoria parietina, and the phycobiont, Trebouxia decolorans, of the lichen X. parietina have been cultured separately and their sterols analysed. X. parietina contained ergosterol and lichesterol as the major constituents together with lower levels of three other C₂₈ sterols. Culture of the mycobiont in the presence of [CD₃]-methionine resulted in the incorporation of two deuterium atoms into the C-24 methyl group of these sterols demonstrating that a 24-methylene intermediate was produced as occurs in other fungi. The phycobiont, T. decolorans contained predominantly poriferasterol with lower levels of clionasterol, ergost-5-en-3β-ol, brassicasterol and cholesterol. Two other Trebouxia spp. (213/3 and 219/2) contained similar sterol mixtures.     

Metabolism of 24-dihydrolanosterol in Ochromonas malhamensis and Chlorella ellipsoidea

24-Dihydrolanosterol-[2-³H] was converted to cholesterol in Chlorella ellipsoidea but ergost-5-enol, poriferasterol, clionasterol were not labelled. The absence of the necessary 24(25) double bond precursor eliminates the possibility of C₂₈ and C₂₉ sterol synthesis. However, it was confirmed that 24-dihydrolanosterol was metabolized by Ochromonas malhamensis to give cholesterol, brassicasterol, and poriferasterol.