Sterol composition of two freshwater molluscs of genusDiplodom

The sterol composition of two taxonomically related freshwater species,Diplodom patagonicus andDiplodom variabilis, respectively, from Lake Nahuel Huapi and the Río de la Plata river were studied by gas liquid chromatography and mass spectrometry. Cholesterol was the main sterol in both species and it was followed by 24-methylcholesta-5, 22-dien-3β-ol, 24-methylcholest-5-en-3β-ol, 24-ethylcholesta-5,22-dien-3β-ol and 24-ethylcholest-5-en-3β-ol. The river species collected within the proximity of marine influence showed less cholesterol and more 24-methylcholesta-5,22-dienol, 24-methylcholest-5-enol and 24-ethylcholesta-5,22-dienol than the lake species.     

Sterols of the spongeTethya amamensis: Occurrence of (24E)-24-ethylidenecholesta-5,7-dienol, (24E)-24-propylidenecholesta-5,7-dienol,and (24Z)-24-propylidenecholesta-5,7-dienol

The spongeTethya amamensis, collected from Kagoshima Bay, Japan, contained at least 24 sterols, including Δ⁵-sterols (82.2% of total sterols) and Δ^{5, 7}-sterols (17.8%). The predominant sterols were cholesterol (29.0%), cholesta-5,22-dienol (13.8%), 24-methylcholesta-5,22-dienol (10.9%), 24-methylenecholesterol (8.3%), 24-methylcholesta-5,7,22-trienol (6.8%), 24-ethylcholest-5-enol (6.1%), and isofucosterol *4.1%). Combined gas liquid chromatography-mass spectrometry suggested the presence of 3 uncommon sterols, (24E)-24-ethylidenecholesta-5,7-dienol, (24E)-24-propylidenecholesta-5,7-dienol, and (24Z)-24-propylidenecholesta-5,7-dienol as minor components. The sterols ofT. amamensis also contained small amounts of 24-norcholesta-5,7,22-trienol and (24Z)-24-ethylidenecholesta-5,7-dienol.     

Sterols ofChaetoceros andSkeletonema

Dietary sterol is required by the oyster for growth, and sterol is believed to be obtained primarily from dietary phytoplankton. Seven isolates ofChaetoceros and one ofSkeletonema, which are of potential use as oyster food, were analyzed for sterol composition using gas chromatography, high-performance liquid chromatography and gas chromatography/mass spectrometry.Skeletonema and five isolates ofChaetoceros contained cholesterol as their major sterol. Two other isolates ofChaetoceros also contained cholesterol, but 24-methylenecholesterol was the principal sterol. Cholesterol has rarely been reported as the major sterol from phytoplankton. In view of the widespread occurrence ofSkeletonema andChaetoceros in the marine environment, these algae could be an important source of the oyster's cholesterol.     

Dealkylation of various 14-alkylsterols by the nematodeCaenorhabditis elegans

The metabolism of 4 dietary 24-alkylsterols was investigated in the free-living nematodeCaenorhabditis elegans. The major unesterified sterols ofC. elegans in media supplemented with either campesterol, 22-dihydrobrassicasterol or stigmasterol included cholesta-5,7-dienol, cholesterol, cholest-7-enol, and 4α-methylcholest-8(14)-enol. Dietary stigmastanol yielded cholest-7-enol, cholestanol, cholest-8(14)-enol, and 4α-methylcholest-8(14)-enol as major unesterified sterols. Esterified sterols comprised less than 22% of the total sterol. Removal of a C-24 ethyl substituent of sterols was neither hindered by the presence of a Δ²²-bond in the sterol side chain nor was it depedent on unsaturation in ring B of the steroid nucleus.C. elegans reduced a Δ²²-bond during its metabolism of stigmasterol; it did not introduce a Δ²²-bond during stigmastanol metabolism.C. elegans was capable of removing a C-24 methyl substituent regardless of its stereochemical orientation. Metabolic processes involving the steroid ring system of cholesterol (C-7 dehydrogenation, Δ⁵-bond, 4α-methylation, Δ⁸⁽¹⁴⁾-isomerization inC. elegans were not hindered by the presence of a 24-methyl group; various 24-methylsterol metabolites from campesterol were detected, mostly 24-methylcholesta-5,7-dienol. In contrast, no 24-ethylsterol metabolites from the dietary ethylsterols were found. More dietary 24-methylsterol remained unmetabolized than did dietary 24-ethylsterol. A 24α-ethyl group and a 24β-methyl group were dealkylated to a greater extent byC. elegans than was a 24α-methyl group, perhaps reflecting the substrate specificity of the dealkylation enzyme system, or suggesting different enzymes altogether.     

Utilization and metabolism of dietary sterols in the honey bee and the yellow fever mosquito

The honey bee,Apis mellifera, does not convert C₂₈ and C₂₉ phytosterols to cholesterol as found in most previous studies of phytophagous or omnivorous insects, but instead the workers and queens selectively transfer 24-methylenecholesterol, sitosterol and isofucosterol from their endogenous sterol pools to the brood larvae regardless of the sterol in the worker diet. Administering radiolabeled sterols by feeding and injection has made it possible to trace this selective transfer through a second generation of the honey bee. In further comparative sterol metabolism studies, the yellow fever mosquito,Aedes aegypti, was shown to be capable of dealkylating and converting a radiolabeled C₂₉ dietary sterol ([¹⁴C] sitosterol) to cholesterol. Metabolic studies with several radiolabeled dietary sterols and an inhibitor of steroid metabolism in the yellow fever mosquito further verified this capability.     

Sterol composition of ungerminated and germinated spores of the Vesicular-Arbuscular Mycorrhizal fungus,Glomus caledonius

The sterol composition of spores of the Vesicular-Arbuscular Mycorrhiza,Glomus caledonius, have been examined by combined gas liquid chromatography-mass spectrometry (GLC-MS). The sterols identified were cholesterol, 24-methylcholesterol, 24-methylenecholesterol and 24-ethylcholesterol. The sterols 24-methylcholesterol, 24-methylenecholesterol and 24-ethylcholesterol have not previously been reported as components of fungi in the Zygomycotina. The spores were germinated on agar and the major changes in sterol esters, free and bound sterols were studied over a period of 21 days. The total sterol content continually increased during the growth period; 24-methylcholesterol and cholesterol were shown to be the major sterols.     

Unusual tetraene sterols in some phytoplankton

Sterols were analyzed from four phytoplankton strains which are under investigation as possible sources of food for oysters in culture. One strain ofPyramimonas contained only 24-methylenecholesterol as a major sterol component.Pyramimonas grossii, Chlorella autotrophica andDunaliella tertiolecta each contained a complex mixture of C₂₈ and C₂₉ sterols with Δ⁷, Δ^5,7 and Δ^5,7,9(11) nuclear double bond systems. Sterols were found both with and without the C-22 side chain double bond. Ergosterol and 7-dehydroporiferasterol were the principal sterols in each of the latter three species, which also contained the rare tetraene sterols, 24-methylcholesta-5,7,9(11),22-tetraen-3β-ol and 24-ethylcholesta-5,7,9(11),22-tetraen-3β-ol.     

Sterols of the oyster,Crassostrea virginica

A commericial sample of the oyster,Crassostrea virginica, obtained from Maryland waters of the Chesapeake Bay, contained 31 desmethylesterols and at least eight 4-monomethylsterols. The combined gas liquid chromatography-mass spectra of the minor components showed the presence of 6 unusual sterols, 24-ethylcholest-22-en-3β ol, 4α-methyl-24-ethylcholestan-3β-ol, occelasterol, (24E)-24-propylidene-cholest-5-en-3β-ol, (24ZO-24-propylidene-cholest-5-en-3β-ol, and 24-methylene-cholestanol. The C-24 configuration of 24-ethylcholest-5-enol, 24-methyl-cholesta-5,22-dienol, and 24-ethylcholesta-5,22 dienol were elucidated by 220 MHz nuclear magnetic resonance spectrometry.     

Identification of the free and conjugated sterol in a non-photosynthetic diatom,Nitzschia alba,as 24-methylene cholesterol

Previous studies on the sterol fraction of the nonphotosynthetic marine diatom,Nitszchia alba, indicated the major sterol to be either brassicasterol (24R-methylcholesta-5,22-dien-3β-ol) or 22-dehydrocampesterol (24S-methylcholesta-5,22-dien-3β-ol) on the basis only of gas chromatographymass spectral analysis. The present studies using nuclear magnetic resonance, infrared, and gas chromatography-mass spectrometry on the free and bound sterol fractions isolated by preparative thin layer chromatography showed the presence in both fractions of a single sterol, with spectral and chromatographic properties identical with those reported for 24-methylenecholesterol (ergosta-5,24(28)-dien-3β-ol). This sterol may be the precursor of 24-methyl sterols found in diatoms. The bound sterol fraction was found to consist of a single compound identified as 24-methylenecholesterol sulfate. No sterol esters or sterol glycosides were detected. Presented at symposium on Marine Lipids, AOCS Meeting, New York, May 1977.     

Chemical association in symbiosis sterol donors in planthoppers

The role of intracellular symbionts contributing to their host has been investigated in the planthoppers,Nilaparvata lugens Stal andLaodelphax striatellus Fallen. We have found that the isolated yeastlike symbionts, identified as a member of the genusCandida, from the host's egg produce ergosterol when cultured. A comparative study of sterols in the cultured symbionts, the host insects, aposymbiotic host insects, and dietary plants demonstrated that ergosterol produced in the symbiotes is provided to the host insects and possibly transformed in the host insects into cholesterol via 24-methylenecholesterol. The conversion of injected 24-methylenecholesterol-d₃ into cholesterol has been shown in the brown planthopper (N. lugens).     

Sterol compositions of seeds and mature plants of family cucurbitaceae

The sterol fractions of the unsaponifiable lipids obtained from 32 seed and mature plant (leaves and stems, pericarp of the fruit, and roots) materials from the 12 generaApodanthera, Benincasa, Citrullus, Coccinea, Cucumis, Cucurbita, Gynostemma, Lagenaria, Luffa, Momordica, Sechium andTrichosanthes, of the family Cucurbitaceae were investigated by gas liquid chromatography (GLC) on an OV-17 glass capillary column. Among the 23 sterols with Δ⁵-, Δ⁷- and Δ⁸-skeletons identified by GLC, the Δ⁷-sterols were found to be the major sterols of most of the Cucurbitaceae investigated. The seed materials contained 24-ethyl-Δ⁷-sterols possessing Δ²⁵-bonds, i.e. 24-ethylcholesta-7,25-dienol and 24-ethylcholesta-7,22,25-trienol, whereas the mature plant materials contained 24-ethyl-Δ⁷sterols without a Δ²⁵-bond, i.e. 24-ethylcholest-7-enol and 24-ethylcholesta-7,22-dienol, as the most predominant sterols, with a few exceptions. The isolation and identification of 24α-ethylcholesta-8(14),22-dienol from the aerial parts ofCucumis sativus also is described.     

A new cytotoxic fatty acid (5<Emphasis Type="Italic">Z</Emphasis>,9<Emphasis Type="Italic">Z</Emphasis>)-22-methyl-5,9-tetracosadienoic acid and the sterols from the far Eastern sponge <Emphasis Type="Italic">Geodinella robusta</Emphasis>

A new fatty acid, (5Z,9Z)-22-methyl-5,9-tetracosadienoic acid (1a), and a rare fatty acid, (5Z,9Z)-23-methyl-5,9-tetracosadienoic acid (2a), the predominant constituents of the free fatty acid fraction from the lipids of the sponge Geodinella robusta, were isolated and partly separated by reversed phase high-performance liquid chromatography, followed by multifold crystallization from MeOH to give 1a and 2a in 70% and 60% purity, respectively. These fatty acids were identified as (5Z,9Z)-22-and (5Z,9Z)-23-methyl-5,9-tetracosadienoic acids by nuclear magnetic resonance techniques, including distortionless enhancement by polarization transfer, heteronuclear multiple quantum connectivity, and correlation spectroscopy experiments, as well as from mass-spectrometric data for their methyl esters, the methyl esters of their perhydro derivatives, and their pyrrolidides. Mixtures of 1a and 2a showed cytotoxic activity against mouse Ehrlich carcinoma cells and a hemolytic effect on mouse erythrocytes. The sterol fraction from the same sponge was analyzed by gas liquid chromatography mass spectrometry, and 24-methylenecholesterol was identified as a main constituent of this fraction. The implications of the co-occurrence of membranolytic long-chain fatty acids and 24-methylenecholesterol as a main membrane sterol are discussed in terms of the phenomenon of biochemical coordination.     

Selective sterol transfer in the honey bee: Its significance and relationship to other hymenoptera

The honey bee,Apis mellifera, is one of only a few species of phytophagous insects known to be unable to convert C-24 alkyl phytosterols to cholesterol. Regardless of the dietary sterols available to worker bees, the major tissue sterol of brood reared by the workers is always 24-methylenecholesterol, followed by sitosterol and isofucosterol. Normally, little or no cholesterol is present in honey bee sterols. The maintenance of high levels of certain sterols is accomplished through a selective transfer of sterols from the endogenous sterol pools of the workers to the developing larvae through the brood food material secreted from the hypopharyngeal and mandibular glands and/or the honey stomach of the workers. The selective uptake and transfer of radiolabeled C₂₇, C₂₈ and C₂₉ sterols have been studied to correlate these aspects of sterol utilization with the discovery of an unusual molting hormone (ecdysteroid) in honey bee pupae as the major ecdysteroid of this stage of development. The phylogenetic implications of this selective transfer phenomenon in the honey bee and comparison with sterol metabolism in certain other hymenopteran species emphasize the diversity of steroid biochemistry in insects.     

Inhibition of C28 and C29 phytosterol metabolism by N,N-dimethyldodecanamine in the nematodecaenorhabditis elegans

Effects on the metabolism of campesterol and stigmasterol inCaenorhabditis elegans were investigated using N,N-dimethyldodecanamine, a known inhibitor of growth, reproduction and the Δ²⁴-sterol reductase of this nematode. 7-Dehydrocholesterol was the predominant sterol (51%) ofC. elegans grown in stigmasterol-supplemented media, whereas addition of 25 ppm amine resulted in a large decrease in the relative percentage of 7-dehydrocholesterol (23%) and the accumulation of a substantial proportion (33%) of Δ²⁴-sterols (e.g., cholesta-5,7,24-trienol) and Δ^22,24-sterols (e.g., cholesta-5,7,22, 24-tetraenol) but yielded no Δ²²-sterols. Dealkylation of stigmasterol byC. elegans proceeded in the presence of the Δ²²-bond; reduction of the Δ²²-bond occurred prior to Δ²⁴-reduction. Addition of 25 ppm amine to campesterol-supplemented media altered the sterol composition ofC. elegans by increasing the percentage of unmetabolized dietary campesterol from 39 to 60%, decreasing the percentage of 7-dehydrocholesterol from 26 to 12%, and causing the accumulation of several Δ²⁴-sterols (6%).C. elegans also was shown to be capable of dealkylating a Δ²⁴⁽²⁸⁾-sterol as it converted 24-methyl-enecholesterol to mostly 7-dehydrocholesterol. The proposed role of 24-methylenecholesterol as an intermediate between campesterol and 7-dehydrocholesterol was supported by the results.     

Comparative studies of metabolism of 4-desmethyl, 4-monomethyl and 4,4-dimethyl sterols inManduca sexta

To investigate the metabolism and possible deleterious effects of 4-methyl and 4,4-dimethyl steroids inManduca sexta, the 4,4-dimethyl sterols lanosterol and cycloartenol, the 4-methyl sterol obtusifoliol and the 4,4-dimethyl pentacyclic triterpenoid α-amyrin were fed in an artificial agar-based diet at various concentrations. Utilization and metabolism of these four compounds were compared with sitosterol, stigmasterol, brassicasterol, ergosterol and 24-methylenecholesterol, 24-alkyl sterols that are readily dealkylated and converted to cholesterol inManduca and in most phytophagous insects. None of the 4-methylated compounds significantly inhibited development except at very high dietary concentrations. The Δ²⁴-bonds of lanosterol and cycloartenol were effectively reduced by theManduca Δ²⁴-sterol reductase enzyme, as is the Δ²⁴-bond of desmosterol which, in most phytophagous insects, is an intermediate in the conversion of sitosterol, stigmasterol and other C₂₈ and C₂₉ phytosterols to cholesterol. On the other hand, the 24-methylene substituent of obtusifoliol was not dealkylated. Each of the 4-desmethyl C₂₈ and C₂₉ sterols was readily converted to cholesterol, and a significant amount of 7-dehydro-cholesterol was derived from ergosterol metabolism. The reason for the differences in substrate specificity of these sterols is not clear, but the information may be useful in the development of new, specific, mechanism-based inhibitors of sterol metabolism.     

Analysis of sterol fractions from twenty vegetable oils

The unsaponifiables separated from 20 vegetable oils were divided into sterol and three other (less polar compound, triterpene alcohol, and 4-methylsterol) fractions by preparative thin layer chromatography. The amounts of the sterol fractions were more than ca. 30% in the unsaponifiables from all of the oils, except tohaku, pumpkin seed, and fagara seed oils. Composition of the sterol fractions were determined by gas liquid chromatography. Individual components of the sterol fractions were identified by gas liquid chromatography and combined gas liquid chromatography-mass spectrometry. β-Sitosterol was found as the most predominant component in the sterol fractions from all oils, except two, i.e. the sterol fraction from pumpkin seed oil contained no detectable amount of β-sitosterol and the sterol fraction from akamegashiwa oil contained Δ⁵-avenasterol as the most abundant component. Campesterol, stigmasterol, Δ⁵-avenasterol, Δ⁷-stigmastenol, and Δ⁷-avenasterol and also trace amounts (at the very least) of cholesterol and brassicasterol were found in most of the oils analyzed. It may be noted that a large amount (ca. 9%) of cholesterol was detected in the sterol fraction from capsicum seed oil. The presence of 24-methylenecholesterol and Δ⁵-avenasterol in the sterol fraction of akamegashiwa oil was demonstrated by isolation of these sterols.     

Biosynthesis of sterols and ecdysteroids in Ajuga hairy roots

Hairy roots of Ajuga reptans var. atropurpurea produce clerosterol, 22-dehydroclerosterol, and cholesterol as sterol constituents, and 20-hydroxyecdysone, cyasterone, isocyasterone, and 29-norcyasterone as ecdysteroid constituents. To better understand the biosynthesis of these steroidal compounds, we carried out feeding studies of variously ²H- and ¹³C-labeled sterol substrates with Ajuga hairy roots. In this article, we review our studies in this field. Feeding of labeled desmosterols, 24-methylenecholesterol, and ¹³C₂-acetate established the mechanism of the biosynthesis of the two C₂₉-sterols and a newly accumulated codisterol, including the metabolic correlation of C-26 and C-27 methyl groups. In Ajuga hairy roots, 3α-, 4α-, and 4β-hydrogens of cholesterol were all retained at their original positions after conversion into 20-hydroxyecdysone, in contrast to the observations in a fern and an insect. Furthermore, the origin of 5β-H of 20-hydroxyecdysone was found to be C-6 hydrogen of cholesterol exclusively, which is inconsistent with the results in the fern and the insect. These data strongly support the intermediacy of 7-dehydrocholesterol 5α,6α-epoxide. Moreover, 7-dehydrocholesterol, 3β-hydroxy-5β-cholest-7-en-6-one (5β-ketol), and 3β,14α-dihydroxy-5β-cholest-7-en-6-one (5β-ketodiol) were converted into 20-hydroxyecdysone. Thus, the pathway cholesterol→7-dehydrocholesterol→7-dehydrocholesterol 5α,6α-epoxide→5β-ketol→5β-ketodiol is proposed for the early stages of 20-hydroxyecdysone biosynthesis. 3β-Hydroxy-5β-cholestan-6-one was also incorporated into 20-hydroxyecdysone, suggesting that the introduction of a 7-ene function is not necessarily next to cholesterol. C-25 Hydroxylation during 20-hydroxyecdysone biosynthesis was found to proceed with ca. 70% retention and 30% inversion. Finally, clerosterol was shown to be a precursor of cyasterone and isocyasterone.     

Evidence for multiple sterol methyl transferase pathways in <Emphasis Type="Italic">Pneumocystis carinii</Emphasis>

The sterol composition of Pneumocystis carinii, an opportunistic pathogen responsible for life-threatening pneumonia in immunocompromised patients, was determined. Our purpose was to identify pathway-specific enzymes to impair using sterol biosynthesis inhibitors. Prior to this study, cholesterol 15 (ca. 80% of total sterols), lanosterol 1, and several phytosterols common to plants (sitosterol 31, 24α-ethyl and campesterol, 24α-methyl 30) were demonstrated in the fungus. In this investigation, we isolated all the previous sterols and many new compounds from P. carinii by culturing the microorganism in steroid-immunosuppressed rats. Thirty-one sterols were identified from the fungus (total sterol=100 fg/cell), and seven sterols were identified from rat chow. Unusual sterols in the fungus not present in the diet included, 24(28)-methylenelanosterol 2; 24(28)E-ethylidene lanosterol 3; 24(28)Z-ethylidene lanosterol 4; 24β-ethyllanosta-25(27)-dienol 5; 24β-ethylcholest-7-enol 6; 24β-ethylcholesterol 7; 24β-ethylcholesta-5,25(27)-dienol 8; 24-methyllanosta-7-enol 9; 24-methyldesmosterol 10; 24(28)-methylenecholest-7-enol 11; 24β-methylcholest-7-enol 12; and 24β-methylcholesterol 13. The structural relationships of the 24-alkyl groups in the sterol side chain were demonstrated chromatographically relative to authentic specimens, by MS and high-resolution ¹H NMR. The hypothetical order of these compounds poses multiple phytosterol pathways that diverge from a common intermediate to generate 24β-methyl sterols: route 1, 1→2→11→12→13; route 2, 1→2→9→10→13; or 24β-ethyl sterols: route 3, 1→2→4→6→7; route 4, 1→2→5→8→7. Formation of 3 is considered to form an interrupted sterol pathway. Taken together, operation of distinct sterol methyl transferase (SMT) pathways that generate 24β-alkyl sterols in P. carinii with no counterpart in human biochemistry suggests a close taxonomic affinity with fungi and provides a basis for mechanism-based inactivation of SMI enzyme to treat Pneumocystis pneumonia.     

Sterol composition and biosynthesis in sorghum: Importance to developmental regulation

Sterol composition and biosynthesis have been examined in seeds, germinating seeds and blades from fally matured leaves ofSorghum bicolor in various stages of development’from seedlings (seven-day plants) to flowering (66-day) plants. The profile of the dominant free sterols of seeds was similar to that of leaf blades; both contained cholesterol, 24α-methylcholesterol (campesterol), 24β-methylcholesterol (dihydrobrassicasterol), 24α-ethylcholesterol (sitosterol) and 24α-ethylcholesta-5,22-dienol (stigmasterol). Sufficient sterol intermediates were identified in the plant to indicate separate post-cycloartenol pathways to sterolic end products. The total free sterol content of the seed (μg/seed) increased somewhat during the 20 hr germination period. However, as the plant developed (seven to 48 days), there was a logarithmic increase in the leaf blade sterol content (μg/leaf blade) which plateaued at the onset of floral differentiation (ca. day 41). Over the next 18 days (48 to 66 days—period of inflorescense development), the sterol content rapidly decreased. In the early stages of plant development, the leaf blade pentacyclic triterpenoid (PT) content was negligible. With the onset of floral differentiation, PT content increased logarithmically, reaching a plateau level that surpassed the sterol content as flowering progressed. These results imply that a critical mass of sterol is associated with sorghum for floral induction. Sterol loss from the leaves of the flowering plants presumably was compensated for by the diversion of 2,3-oxidosqualene (SO) from sterol synthesis to PT production. Additional feeding and trapping experiments with [2-¹⁴C]mevalonic acid, [2-³H]cycloartenol, [24-³H]lanosterol [4-¹⁴C]sitosterol and [4-¹⁴C]cholesterol fed to germinating seeds and leaves from flowering plants demonstrated that sorghum possessed a cycloartenolbased pathway; germinating seeds synthesized 24-alkylsterols but not cholesterol, although cholesterol was identified in both dry and germinating seeds by gas chromatography-mass spectroscopy (GC-MS); and mature leaves synthesized cholesterol and 24α-alkylsterols but not 24β-methylcholesterol.     

Sterols of eustigmatophytes

The oyster cannot synthesize sterols from smaller molecules but must obtain them from its diet, which consists of detritus and small organisms, i.e., mostly single-celled algae. Algae differ widely in their effectiveness as oyster food. Small (<5 μm) algae which are abundant in sterols and polyunsaturated fatty acids appear to be most effective. Recent studies have shown the occurrence of cholesterol in strains of the unicellular algaeTetraselmis, Chaetoceros andSkeletonema, sometimes in large quantities. In the study reported here, six isolates of a recently constructed algal class, the Eustigmatophyceae, have been examined for sterols and fatty acids by gas chromatography and gas chromatography/mass spectrometry. All strains were shown to contain cholesterol as the principal sterol. Two isolates contained large amounts of total sterol (400–1000 fg/cell), and one (Sticho 0–18) also contained large amounts of eicosapentaenoic acid (20∶5n−3). These biochemical characteristics are desirable in a potential food source for oysters.