Sterols of morphologically distinct,okadaic acid-producing Prorocentrum texanum var. texanum and var. cuspidatum isolated from the Gulf of Mexico

Prorocentrum texanum var. texanum and its morphologically distinct yet genetically identical (as based on the sequences of five genes) variety P. texanum var. cuspidatum represent a species of Prorocentrum recently isolated from the Gulf of Mexico. Together, these two varieties represent a sister species to Prorocentrum micans. P. micans has had its sterols, which are ringed lipids common to eukaryotic cell membranes, shown in some studies to be comprised of cholesterol (cholest-5-en-3β-ol), 23,24-dimethyl-cholesta-5,22-dien-3β-ol, 23,24-dimethyl-5α-cholest-22E-en-3β-ol, dinosterol, and 4α,23,24-trimethyl-5α-cholestan-3β-ol (dinostanol) as major sterols, thus placing it within a previously identified cluster of dinoflagellates characterized by the predominance of cholesterol and dinosterol. In this study we have determined the sterol compositions of these two varieties of P. texanum to be abundant in cholesterol, 23,24-dimethyl-cholesta-5,22-dien-3β-ol, 23,24-dimethyl-5α-cholest-22E-en-3β-ol, dinosterol, and dinostanol such that the varieties are virtually indistinguishable from each other, making them both in general agreement with the sterols of P. micans, its closest species relative. This expands our knowledge of the sterols of this environmentally important dinoflagellate genus.     

STEROL DISTRIBUTION IN THE GENUS HETEROCAPSA (PYRRHOPHYTA)1

The sterol composition of seven strains of marine peridinioid dinoflagellates comprising the four known species of Heterocapsa Stein was examined by gas chromatography-mass spectrometry to determine the utility of these compounds in systematics. Cholest-5-en-3β-ol (cholesterol), 24-methyl-cholest-5-en-3β-ol (24-methylcholesterol), 4α,24(S)-dimethyl-5α-cholestan-3β-ol (4,24-dimethylcholestanol), 4α,23,24(R)-trimethyl-5α-cholest-22-en-3β-ol (dinosterol), 4α,23ξ,24ξ-trimethyl-5α-cholestan-3β-ol (dihydrodinosterol), and an unknown sterol were detected. Sterol composition does not vary significantly from species to species within the genus Heterocapsa and thus cannot be used for species differentiation. Sterols may, however, have value in defining the properties of dinoflagellate taxa above the family level. Over the course of the growth curve for Heterocapsa niei (Loeblich) Morrill & Loeblich 4,24-dimethylcholestanol and dinosterol covaried, suggesting that 4,24-dimethylcholestanol is converted into dinosterol by a previously proposed bioalkylation scheme.     

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.     

Analysis of sterols in selected bloom-forming algae in China

Sterols, a group of stable lipid compounds, are often used as biomarkers in marine biogeochemical studies to indicate sources of organic matter. In this study, sterols in 13 species of major bloom-forming algae in China, which belong to Dinophyceae, Bacillariophyceae, Ulvophyceae, and Pelagophyceae, were analyzed with gas chromatography-mass spectrometry (GC–MS) to test their feasibility in representing different types of harmful algal blooms (HABs). It was found that (24Z)-stigmasta-5,24-dien-3β-ol (28-isofucosterol) was a major sterol component in green-tide forming macroalga Ulva prolifera. In bloom-forming dinoflagellates Alexandrium spp., Prorocentrum micans and Scrippsiella trochoidea, (22E)-4α,23-dimethyl-5α-ergost-22-en-3β-ol (dinosterol) was detected in addition to cholest-5-en-3β-ol (cholesterol), (22E)-ergosta-5,22-dien-3β-ol, (22E)-stigmasta-5,22-dien-3β-ol and other minor sterol components. In brown-tide forming pelagophyte Aureococcus anophagefferens, (24E)-24-propylcholesta-5,24-dien-3β-ol ((24E)-24-propylidenecholesterol) and (24Z)-24-propylcholesta-5,24-dien-3β-ol ((24Z)-24-propylidenecholesterol) were detected together with cholesterol, (22E)-stigmasta-5,22-dien-3β-ol, stigmast-5-en-3β-ol and campest-5-en-3β-ol. Among the selected bloom-forming diatoms, Chaetoceros sp. and Pseudo-nitzschia spp. only produced cholesterol, while Cylindrotheca closterium produced solely (22E)-ergosta-5,22-dien-3β-ol. Sterol content in four bloom-forming algal species correlates well with their biomass or abundance. It's proposed that 28-isofucosterol could serve as a promising biomarker for green algae in green-tide studies. Dinosterol and (24Z)-24-propylidenecholesterol can be used as potential biomarkers to represent bloom-forming dinoflagellates and pelagophytes, while (22E)-ergosta-5,22-dien-3β-ol is not a good indicator for diatoms.     

Novel dinoflagellate 4α-methylated sterols from four caribbean gorgonians

Fourteen 4α-methyl sterols have been isolated from the gorgonians Briareum asbestinum, Gorgonia mariae, Muriceopsis flavida and Pseudoplexaura wagenaari, including the following five new sterols: 4α-methyl-24-methylene-5α-cholestan-3β-ol, (24R)-4α, 24-dimethyl-5α-cholesta-7,22-dien-3,β-ol, 4α,24S(or 23ξ)-dimethyl-5α-cholest-7-en-3β-ol, (22E, 24R)-4α,23,24-trimethyl-5α-cholesta-7,22-dien-3β-ol and (24R)-4α,24-dimethyl-5α-cholesta-8(14),22-dien-3β-ol. There is strong evidence that these 4α-methyl sterols are synthesized by the algal (dinoflagellate) symbionts (zooxanthellae) of the gorgonians. It is suggested that analysis of 4Δ-methyl sterol mixtures isolated from a zooxanthellae-bearing invertebrate, collected in several different geographic locations, might give information on the specificity of the symbiotic association between a given animal species and a particular strain of zooxanthellae.     

Effect of ay-9944 on sterol biosynthesis in Chlorella sorokiniana

When Chlorella sorokiniana was grown in the presence of 4 ppm AY-9944 total sterol production was unaltered in comparison to control cultures. However, inhibition of sterol biosynthesis was shown by the accumulation of a number of sterols which were considered to be intermediates in sterol biosynthesis. The sterols which were found in treated cultures were identified as cyclolaudenol, 4α,14α-dimethyl-9β,19-cyclo-5α-ergost-25-en-3β-ol, 4α,14α-dimethyl -5α-ergosta-8,25-dien-3β-ol, 14α-methyl-9β,19-cyclo-5α-ergost-25-en-3β-ol, 24-methylpollinastanol, 14α-methyl-5α-ergost-8-en-3β-ol, 5α-ergost -8(14)-enol, 5α-ergost-8-enol, 5α-ergosta-8(14),22-dienol, 5α-ergosta-8,22-dienol, 5α-ergosta-8,14-dienol, and 5α-ergosta-7,22-dienol, in addition to the normally occurring sterols which are ergosterol, 5α-ergost-7-enol, and ergosta-5,7-dienol.The occurrence of these sterols in the treated culture indicates that AY-9944 is an effective inhibitor of the Δ⁸ → Δ⁷ isomerase and Δ¹⁴-reductase, and also inhibits introduction of the Δ²²-double bond. The occurrence of 14α-dimethyl-5α-ergosta-8,25-dien-3β-ol and 14α-methyl-9β,19-cyclo-5α-ergost -25-en-3β-ol is reported for the first time in living organisms. The presence of 25-methylene sterols suggests that they, and not 24-methylene derivatives, are intermediates in the biosynthesis of sterols in C. sorokiniana.     

Sterols of Testudodinium testudo (formerly Amphidinium testudo): Production of the Δ8(14) sterol gymnodinosterol and chemotaxonomic relationship to the Kareniaceae

Testudodinium testudo is a peridinin-containing dinoflagellate recently renamed from Amphidinium testudo. While T. testudo has been shown via phylogenetic analysis of small subunit ribosomal RNA genes to reside in a clade separate from the genus Amphidinium, it does possess morphological features similar to Amphidinium sensu stricto. Previous studies of Amphidinium carterae and Amphidinium corpulentum have found the sterols to be enriched in Δ⁸⁽¹⁴⁾ sterols, such as 4α-methyl-5α-ergosta-8(14),24(28)-dien-3β-ol (amphisterol), uncommon to most other dinoflagellate taxa and thus considered possible biomarkers for the genus Amphidinium. Here, we provide an examination of the sterols of T. testudo and show they are dominated not by amphisterol, but rather by a different Δ⁸⁽¹⁴⁾ sterol, (24R)-4α-methyl-5α-ergosta-8(14),22-dien-3β-ol (gymnodinosterol), previously thought to be a major sterol only within the Kareniaceae genera Karenia, Karlodinium, and Takayama. Also found to be present at low levels were 4α-methyl-5α-ergosta-8,14,22-trien-3β-ol, a sterol previously observed in Karenia brevis to be an intermediate in the production of gymnodinosterol, and cholesterol, a sterol common to many other dinoflagellates. The presence of gymnodinosterol in T. testudo is the first report of this sterol as the sole major sterol in a dinoflagellate outside of the Kareniaceae. The implication of this chemotaxonomic relationship to the Kareniaceae is discussed.     

Minor sterols of marine invertebrates 37. Isolation of novel coprostanols and 4α-methyl sterols from the tunicate Ascidia nigra

The complex sterol mixture isolated from $\text{A, nigra}$ was found to contain a low level of Δ⁴-3-keto steroids, 5β-stanols and 4α-methyl sterols in addition to regular (4-demethyl) sterols. The following new marine sterols were isolated and identified using MS and 360 MHz NMR: 5β-cholest-22E-en-3β-ol, 24S-methyl-5β-cholest-22E-en-3β-ol, 24-methylene-5β-cholestan-3β-ol, both epimers at C-24 of 4α-methyl-24-ethyl-5α-cholest-22E-en-3β-ol, 4α, 22ξ, 23ξ-(or 24ξ-)trimethyl-5α-cholest-8(14)-en-3β-ol and (22S, 23S, 24S)-4α-24-dimethyl-22, 23-methylene-5α-cholestan-3β-ol. The latter sterol and 23-demethylgorqosterol have opposite configurations at C-22, C-23, and C-24; the Δ⁸⁽¹⁴⁾ sterol has an unprecedented side chain.     

Sterols with unusual nuclear unsaturation from three cultured marine dinoflagellates

Several new 4α-methyl sterols with unusual unsaturation in the Δ⁸⁽¹⁴⁾-or Δ¹⁴-positions, 4α,24S-dimethyl-5α-cholest-8 (14)-en-3β-ol, 4α-methyl-24ξ-ethyl-5α-cholest-8(14)-en-3β-ol, 4α-methyl-24(Z)-ethylidene-5α-cholest-8(14)- en-3β-ol, 4α,23 (or 22),24ξ-trimethyl-5α-cholesta-8(14),22-dien-3β-ol, 4α,24S(or 23ξ)-dimethyl-5α-cholest-14-en-3β-ol and 14-dehydrodinosterol, have been isolated from extracts of the cultured marine dinoflagellates Amphidinium carterae, A. corpulentum and Glenodinium sp. 4α-Methyl-24ξ-ethyl-5α-cholestan-3β-ol was isolated from the steryl ester fraction of Glenodinium sp. The structures of these new sterols are based upon extensive 360 MHz ¹H NMR and MS analyses.     

Sterols of Amphidinium species in the Operculatum Clade: Predominance of cholesterol instead of Δ8(14) sterols previously considered Amphidinium-specific biomarkers

The dinoflagellates Amphidinium carterae and Amphidinium corpulentum have been previously characterized as having Δ⁸⁽¹⁴⁾-nuclear unsaturated 4α-methyl-5α-cholest-8(14)-en-3β-ol (C_28:1) and 4α-methyl-5α-ergosta-8(14),24(28)-dien-3β-ol (amphisterol; C_29:2) as predominant sterols, where they comprise approximately 80% of the total sterol composition. These two sterols have hence been considered as possible major sterol biomarkers for the genus. Here, we have examined the sterols of four recently identified species of Amphidinium (Amphidinium fijiense, Amphidinium magnum, Amphidinium theodori, and Amphidinium tomasii) that are closely related to Amphidinium operculatum as part of what is termed the Operculatum Clade to show that each species has its sterol composition dominated by the common dinoflagellate sterol cholesterol (cholest-5-en-3β-ol; C_27:1), which is found in many other dinoflagellate genera, rather than Δ⁸⁽¹⁴⁾ sterols. While the Δ⁸⁽¹⁴⁾ sterols 4α-methyl-5α-cholest-8(14)-en-3β-ol and 4α,23,24-trimethyl-5α-cholest-8(14),22E-dien-3β-ol (C_30:2) were present as minor sterols along with another common dinoflagellate sterol, 4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol (dinosterol; C_30:1), in some of these four species, amphisterol was not conclusively observed. From a chemotaxonomic perspective, while this does reinforce the genus Amphidinium's ability to produce Δ⁸⁽¹⁴⁾ sterols, albeit here as minor sterols, these results demonstrate that caution should be used when considering Δ⁸⁽¹⁴⁾ sterols, especially amphisterol, as Amphidinium-specific biomarkers within these species where cholesterol is the predominant sterol.     

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.     

Biosynthesis of Δ5.23 sterols in etiolated coleoptiles from Zea mays

In addition to the previously found ergosta-5, E-23-dien-3β-ol and 5α-ergosta-7, E-23-dien-3β-ol, the following Δ23 sterols have been identified in etiolated maize coleoptiles: cyclosadol, 4α, 14α-dimethyl-5α-ergosta-8, E-23-dien-3β-ol, 4α, 14α-dimethyl-9β, 19-cyclo-5α-ergosta-8, E-23-dien-3β-ol and 4α-methyl-5α-ergosta-7, E-23-dien-3β-ol. The incubation of maize coleoptile microsomes in the presence of cycloartenol and of [¹⁴C-methyl]S-adenosyl methionine gave a mixture of labelled 24-methylene cycloartanol and cyclosadol. No trace of cyclolaudenol could be detected in these conditions. It is suggested that Δ²³ sterols are products of the C-24 methyltransferase reaction and they probably do not arise from a Δ²⁴ → Δ²³ isomerization occurring at a later stage of the biosynthesis. The Δ¹³-sterols may play an intermediary role in the biosynthesis of 24-methyl sterols in this plant material.     

Free sterol composition of species in the dinoflagellate genus Pyrocystis: a spectrum of sterol diversity

The dinoflagellate genus Pyrocystis includes a small number of marine species, which spend the majority of their life cycles as nonmotile cells within a carbohydrate sheath, and which are found ubiquitously throughout the world's oceans. The biochemistry of this model dinoflagellate genus has been widely studied due to its ability to bioluminesce. However, Pyrocystis has been comparatively understudied with respect to its lipid biochemistry, in particular that of sterols. To date, examination of the sterols of Pyrocystis has focused primarily upon Pyrocystis lunula, which produces cholesterol and 4,24-dimethyl-5α-cholestan-3β-ol as its predominant sterols, while it lacks the common dinoflagellate sterol, dinosterol. We have examined the sterol composition of the two other commercially available species of Pyrocystis, Pyrocystis fusiformis and Pyrocystis noctiluca. Pyrocystis noctiluca possesses dinosterol as its most abundant sterol, while P. fusiformis possesses dinosterol and 4,24-dimethyl-5α-cholestan-3β-ol as the predominant sterols, placing it at an intermediate position between P. lunula and P. noctiluca, as based on sterol composition. The potential limitations of the dinoflagellate sterol biomarker dinosterol are also explored in this study due to its notable absence in P. lunula.     

UNUSUAL DIHYDROXYSTEROLS AS CHEMOTAXONOMIC MARKERS FOR MICROALGAE FROM THE ORDER PAVLOVALES (HAPTOPHYCEAE)1

Recent studies have led to the identification of an unusual class of dihydroxysterols (steroidal diols termed “pavlovols”)in a few species of microalgae from the genus Pavlova (family Pavlovaceae, class Haptophyceae = Prymnesiophyceae). These compounds have an additional hydroxyl group at G-4 in the sterol A ring, which appears to be very rare in sterol biosynthetic pathways. The sterol compositions of many other haptophytes from different orders have been analyzed, but to date all have lacked pavlovols. We now report the occurrence of these compounds in Diacronema vlkianum Prauser and two strains of Pavlova pinguis Green. This is the first report of the lipid composition of these species. Both microalgae contained “24-methylpavlovol” (4α, 24-dimethyl-5α-cholestan-3β, 4β-diol), P. pinguis also contained “24-ethylpavlovol” (4α-methyl-24-ethyl-5α-cholestan-3β, 4β-diol), and D. vlkianum contained a diol identified from its mass spectrum as 4α, 24β-dimethyl-5α-cholest-22E-en-3β,4β-diol. Both species contained structurally analogous 4-desmethyl sterols and 4-methyl sterols, although there were major differences in the proportions in each series. The major 4-desmethyl sterol in both species was 24-ethylcholesta-5, 22E-dien-3β-ol and the major 4-methyl sterol was 4α-methyl-24-ethyl-5α-cholest-22E-en-3β-ol. The presence of pavlovols in P. pinguis, combined with earlier data, suggests that all Pavlova species might have this distinguishing lipid feature. However, their identtjication in D. vlkianum extends the occurrence of these compounds to another genus and shows that they are not unique to the genus Pavlova. However, they are probably restricted to species from the order Pavlov ales. The modes of biosynthesis and functions of pavlovols remain unknown.     

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.     

Sterols of the ‘dinotom’ Durinskia baltica (Dinophyceae) are of dinoflagellate origin

‘Dinotoms’ are a relatively small group of dinoflagellates with aberrant tertiary plastids of diatom origin, thus differing from the majority of photosynthetic dinoflagellates which possess the carotenoid pigment peridinin and have secondary plastids of red algal origin. As part of our laboratory's continuing efforts to examine such unusual dinoflagellates in the search for clues to the evolution of their lipid compositions, we have examined the sterol composition of the dinotom Durinskia baltica. As such, we here compared its sterols to those of the previously examined dinotom, Kryptoperidinium foliaceum, more broadly to other photosynthetic, peridinin-containing dinoflagellates, and to the diatom genus Nitzschia, which is the presumed ancestor of the D. baltica dinotom plastid. Sterols are ringed lipids, common to eukaryotes, thought to reinforce phospholipid bilayers. Many peridinin-containing dinoflagellates have sterol compositions which are enriched by the presence of cholesterol (cholest-5-en-3β-ol) and 4α-methyl-substituted sterols such as dinosterol (4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol); this has also been found to be true for K. foliaceum despite its aberrant plastid ancestry. Our objective was to determine if this is also true for D. baltica as only the second dinotom to have its sterols characterized in detail, and to determine if there is any indication of prominent sterols which are uncommon to dinoflagellates, possibly originating from the diatom endosymbiont, as has been demonstrated previously with K. foliaceum and D. baltica chloroplast-associated galactolipids of clear diatom origin. Our results demonstrate that like K. foliaceum, the major sterols of D. baltica are cholesterol, dinosterol, and other 4α-methyl-substituted sterols common to dinoflagellates. Although there were a number of minor sterols, none were found with obvious origin from the diatom endosymbiont, indicating that most originated with the dinoflagellate host itself, most likely before acquisition of the diatom tertiary plastid.     

PIGMENTS,FATTY ACIDS,AND STEROLS OF THE TOXIC DINOFLAGELLATE GYMNODINIUM CATENATUM1

Cultures and field samples of the toxic dinoflagellate Gymnodinium catenatum Graham from Tasmania, Australia, were analyzed for pigment, fatty acid, and sterol composition. Gymnodinium catenatum contained the characteristic pigments of photosynthetic dinoflagellates, including chlorophyll a, chlorophyll c₂, and the carotenoids peridinin, dinoxanthin, diadinoxanthin, diatoxanthin, and β,β-carotene. In midlogarithmic and early stationary phase cultures, the chlorophyll a content ranged 50–72 pg · cell^?1, total lipids 956–2084 pg · cell^?1, total fatty acids 426–804 pg · cell^?1, and total sterols 8–20 pg · cell^?1. The major fatty acids (in order of decreasing abundance) were 16:0, 22:6(n-3), and 20:5(n-3) (collectively 65–70% of the total fatty acids), followed by 16:1(n-7), 18:2(n-6), and 14:0. This distribution is characteristic of most dinoflagellates, except for the low abundance (<3%) of the fatty acid 18:5(n-3), considered by some authors to be a marker for dinoflagellates. The three major sterols were 4α-methyl-5α-cholest-7-en-3β-ol, 4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol (the dinoflagellate sterol, dinosterol), and 4α,23,24-trimethyl-5α-cholest-7-en-3β-ol. These three sterols comprised about 75% of the total sterols in both logarithmic and early stationary phase cultures, and they were also found in high proportions (22–25%) in natural dinoflagellate bloom samples. 4-Desmethyl sterols, which are common in most microalgae, were only present in trace amounts in G. catenatum. The chemotaxonomic affinities of G. catenatum and the potential for using specific signature lipids for monitoring toxic dinoflagellate blooms are discussed.     

Sterols of a diatomaceous ooze from walvis bay

Almost an of the solvent-extractable sterols and their nuclearsaturated analogues in a sample of Walvis Bay surface sediment have been analysed by capillary GLC and GC-MS, and by coinjection with a variety of standards. The presence in sediments of 22-$\text{trans}$-24-nor-5α-cholest-22-en-3β-ol, 24-methylene-5α-cholestan-3β-ol, and components tentatively assigned as 23,24-dimethylcholesta-5,22-dien-3β-ol and 23,24-dimethyl-5α-cholest-22-en-3β-ol has been demonstrated for the first time. A novel sterol and its saturated analogue have also been found. The sterol distribution cannot be related solely to the reported major input of phytoplankton; the presence of 22,23-methylene-23,24-dimethylcholest-5-en-3β-ol and its saturated analogue indicates a coelenterate contribution. The analysis emphasises the necessity of glass capillary columns and coinjection of standards.     

Effect of ageing on sterol metabolism in potato tuber slices

When fresh potato tuber slices were incubated with [1-¹⁴C]-sodium acetate, cycloartenol was heavily labelled but no radioactivity was recovered in 24-methylene cycloartanol and free sterols. If potato slices were aged for 0–24 hr before feeding with radioactive acetate, a rapid increase of the label in the sterol precursors and the free sterols was observed. The free sterol content was 5 × higher after ageing for 24 hr. Isofucosterol synthesis was especially stimulated. The synthesis of sterols during the ageing process seems to be related to the appearance of a cycloartenol C24-methylase and may be linked to a biogenesis of membranes.Nomenclature: (1) 4,4,14α-trimethyl 9β, 19β-cyclo-5α-cholest-24-en 3β-ol; (2) 4,4,14α-trimethyl 9β, 19β-cyclo-5α-ergost-24(28)-en 3β-ol; (3) 4α,14α-dimethyl 9β,19β-cyclo 5α-ergost 24(28)-en 3β-ol; (4) 4α, 14α-dimethyl 5α-ergosta 8.24(28)-dien 3β-ol; (5) 4α-methyl 5α-ergosta 7,24(28)-dien 3β-ol; (6) ergosta 5,24(28)-dien 3β-ol; (7) stigmasta 5,Z-24(28)-dien 3β-ol; (8) (24R)-24 methyl cholest 5-en 3β-ol; (9) (24R)-24 ethyl cholest 5-en 3β-ol; (10) (24S)-24 ethyl cholesta 5,E-22(23)-dien 3β-ol; (11) cholest 5-en 3β-ol.     

THE LIPID COMPOSITION OF THORACOSPHAERA HEIMII: EVIDENCE FOR INCLUSION IN THE DINOPHYCEAE1

The fatty acid, sterol and chlorophyll composition of the calcified, unicellular alga Thoracosphaera heimii (Lohmann) Kamptner are reported. The presence of 4,23,24-termethyl-5α-cholest-22E-en-3β-ol (dinosterol), 4,23,24-trimethyl-5α-cholest-22E-en-3-one (dinosterone) and the predominance of C₁₈, C₂₀ and C₂₂ unsaturated fatty acids, including the acid 18:5ω3, indicates that T. heimii is a dinoflagellate. The fatty acid: sterol ratio (1.3), is typical of dinoflagellates. The geochemical significance of dinosterone, the high relative concentration of 4-desmethyl-5α-stanols and the role of 23-methyl-5α-cholest-22E-en-3β-ol in the biosynthesis of dinosterol in T. heimii are also discussed.