Transcriptional expression characteristics and subcellular localization of ADP-glucose pyrophosphorylase in the oil plant Perilla frutescens

Three ADP-glucose pyrophosphorylase clones were isolated from the cotyledon cDNA library of the oil plant, Perilla frutescens, and their intracellular localization investigated. Two of three cDNAs (PfagpS1 and PfagpS2) were homologous to the catalytic small subunit of AGPases found in other plants, while the third clone (PfagpL) was highly similar to the large subunit type. Transcripts for PfagpS1 and PfagpS2 were observed in both photosynthetic and non-photosynthetic tissue, showing the highest expression in the stem, while PfagpL transcripts were abundantly expressed in stem and cotyledon. To evaluate the subcellular localization of PfagpS2 and PfagpL as well as the maize BT2, N-terminus-GFP DNA fusion were constructed and transformed into tobacco plants. Immunoblot analysis showed that the expressed PfagpS2- and PfagpL-GFP fusions were targeted to the plastid in the heterologous tobacco system whereas the BT2-GFP remained intact, suggesting a cytoplasmic location. These intracellular assignments were confirmed by direct confocal microscopic examination. GFP signals were localized to the cytoplasm as well as in the nucleus in BT2-GFP plants, and to the plastids in PfagpS2- and PfagpL-GFP plants. Our results indicate that Perilla cotyledons contain multiple AGPase subunits, of which at least two isoforms and very likely the third, are plastidial in nature.

Development of a serum-free system for the in vitro cultivation of Brugia malayi infective-stage larvae

Over the past several years, numerous attempts have been made to culture the infective-stage (L3) larvae of the human filarial parasite Brugia malayi in an in vitro system that promotes molting to the fourth larval stage (L4). Although there have been reports in the literature of successful L3 to L4 development in vitro, all of these systems have required serum supplementation. The complexity of serum as a culture supplement has made reproducibility of results and identification of specific factors necessary for L3 development problematic. We have developed a serum-free in vitro system consisting of RPMI 1640 supplemented with one of three fatty acids (arachidonic, linoleic, or linolenic) that supports consistent and reproducible molting to the fourth larval stage in the presence of a basidiomycetous yeast, Rhodotorula minuta. Coculture with this yeast, initially isolated as a culture contaminant, is required for successful molting. In serum-free cultures lacking R. minuta, L3 larvae survive for upward of 2 weeks, but do not molt successfully. The L4 larvae generated in cultures containing R. minuta are well formed, as seen by light and electron microscopy, and are capable of further development upon transfer to a permissive host. This culture system is inexpensive and easily reproducible, thus making it a useful tool for studying the requirements for the development of B. malayi L3.

Influence of linoleic/linolenic acid ratio in the diet of periparturient cattle on plasma concentrations of PGF2 alpha metabolite and placental expulsion rate

Forty-eight cows Holstein Friesian x Dutch Friesian (HF x DF) were randomly assigned to 2 groups fed 1 of 2 diets (isocaloric and isonitrogenous but different in linoleic/linolenic acid ratio) from 4 wk before expected parturition until 7 d after calving. Effects of the diet on plasma linoleic/linolenic acid ratio, plasma PGFM levels and placental explusion rate were studied. Dietary treatment resulted in significant differences in linoleic/linolenic acid ratio in blood plasma (1.00 +/- .22 vs 4.41 +/- .53). The placental expulsion rate was not significantly different between the 2 treatment groups. Plasma PGFM levels, as analyzed for 28 cows from 30 d before parturition until 1.5 d after parturition, were similar for the diets. Cows with a longer placental expulsion rate had lower PGFM levels at parturition (for instance, placental expulsion rate shorter (n = 11) and longer (n = 17) than 6 h, 1248 vs 2965 pg/ml, residual standard deviation 1185 pg/ml, P < 0.01). The results show that the dietary linoleic/linolenic acid ratio can influence the plasma linoleic/linolenic acid ratio without affecting the placental expulsion rate or plasma PGFM levels around parturition.

[3-13C] gamma-linolenic acid: a new probe for 13C nuclear magnetic resonance studies of arachidonic acid synthesis in the suckling rat

Our objective was to develop a suitable probe to study metabolism of polyunsaturated fatty acids by 13C nuclear magnetic resonance (NMR) in the suckling rat pup. [3-13C] gamma-Linolenic acid was chemically synthesized, and a 20 mg (Experiment 1) or 5 mg (Experiment 2) dose was injected into the stomachs of 6-10-day-old suckling rat pups that were then killed over a 192 h (8 d) time course. 13C NMR showed that 13C in gamma-linolenate peaked in liver total lipids by 12-h post-dosing and that [5-13C]-arachidonic acid peaked in both brain and liver total lipids 48-96 h post-dosing. 13C enrichment in brain gamma-linolenic acid was not detected by NMR, but gas chromatography-combustion-isotope ratio mass spectrometry showed that its mass enrichment in brain phospholipids at 48-96 h post-dosing was 1-2% of that in brain arachidonic acid. 13C was present in liver and brain cholesterol and in perchloric acid-extractable water-soluble metabolites in the brain, liver and carcass. We conclude that low but measurable amounts of exogenous gamma-linolenic acid do access the suckling rat brain in vivo. The slow time course of [5-13C] arachidonic acid appearance in the brain suggests most of it was probably transported there after synthesis elsewhere, probably in the liver. Some carbon from gamma-linolenic acid is also incorporated into lipid products other than n-6 long-chain polyunsaturated fatty acids.

Comparative hypocholesterolemic effects of six vegetable oils in cholesterol-fed rat

The hypocholesterolemic efficacies of various polyunsaturated fatty acids were compared in rats given cholesterol-enriched diets. Oenothera biennis Linn oil (OBLO, linoleic + gamma-linolenic), sunflower oil (linoleic), palm oil (PLO, oleic + linoleic), soybean oil (linoleic + alpha-linolenic), high-oleic safflower oil (oleic + linoleic), or mixed oil (linoleic + alpha-linolenic) was added to the diet at 200 g/kg (20% groups). OBLO was also added at 100 g/kg diet (10% group). The serum total and very low density lipoprotein + intermediate lipoprotein + low density lipoprotein cholesterol concentrations of the 10 and 20% OBLO groups were consistently lower than those in the other groups. The liver cholesterol concentration in the PLO group was lower in all groups. The liver cholesterol concentrations in the 10 and 20% OBLO groups were also lower than in the other groups. There were no significant differences in the fecal neutral sterol and bile acid extraction among groups.

Preventive effects of magnesium on raised serum lipid peroxide levels and aortic cholesterol deposition in mice fed an atherogenic diet

We examined the effects of various levels of magnesium intake on serum lipid levels and aortic cholesterol deposition in mice fed for 14 weeks on an atherogenic diet containing 10 per cent linoleic acid. During that time, the mice were given MgCl2.6H2O in drinking water at magnesium doses of 10, 50, 100, or 200 mg/kg/d. A magnesium dose of 50 mg/kg/d is approximately equivalent to the amount consumed in the normal daily diet. Throughout the experimental period, levels of both serum total cholesterol and lipid peroxides decreased relative to increases in the dose of magnesium, while levels of serum phospholipid, triglyceride, and high density lipoprotein (HDL)-cholesterol were unaffected. Levels of aortic cholesterol, particularly cholesteryl ester, decreased as the dose of magnesium increased. These findings indicate that adequate magnesium intake prevents cholesterol deposition in the aortas of mice fed an atherogenic diet, and that this was due to the inhibitory effect of magnesium on lipid peroxidation and its hypocholesterolaemic effect, suggesting in turn, that the antioxidative action of this element plays an important role in creating a defence against the development of atherosclerosis.

Hypochlorous acid-induced zinc release from thiolate bonds: a potential protective mechanism towards biomolecules oxidant damage during inflammation

It has been proposed that metalloprotein zinc mobilization mediated by hypochlorous acid (HOCl) may induce cell injury (see H. Fliss and M. Ménard (1991), Archives of Biochemistry and Biophysics, 287, 175-179). In the present paper, we have demonstrated using a dimercaptopropanol-zinc complex that, once released from thiolate bonds by HOCl, zinc can exert a significant antioxidant effect on both linolenic acid and deoxyribose oxidation induced by iron. In these experimental conditions, however, the antagonism towards deoxyribose oxidation is notably less than that towards linolenic acid peroxidation, thus suggesting a more specific inhibitory effect of zinc on iron-mediated oxidant damage when polyunsaturated fatty acids represent the oxidizable substrate. The antioxidant effects of zinc are strictly related to the "free" form; indeed, the dimercaptopropanol-zinc complex per se is stimulatory even on biomolecules oxidant damage, apparently as a result of the prooxidant prooxidant interaction of the thiol compound with iron. In light of these results, it may be proposed that the zinc released from thiolate bonds by HOCl could specifically limit tissue oxidative burden in pathological conditions involving neutrophil accumulation and activation, such as inflammation and ischemia-reperfusion.

Modulation by dietary oils and clofibric acid of arachidonic acid content in phosphatidylcholine in liver and kidney of rat: effects on prostaglandin formation in kidney

The manipulation of 20:4(n - 6) contents in phosphatidylcholine of liver and kidney of rats by dietary oils and p-chlorophenoxyisobutyric acid (clofibric acid) as well as the effects on the formation of prostaglandin E2 in kidney were studied. Three groups of rats were fed diets that contained either safflower oil (SO) or perilla oil (PO) or fish oil (FO) for 1 week. Each dietary group was divided into two groups. One group continued the same diet for another 1 week; the second group continued the same diet and received subcutaneous injections of clofibric acid once a day for 1 week. The content of 20:4(n - 6) in hepatic phosphatidylcholine was markedly lowered by feeding either FO or PO and was further decreased by the administration of clofibric acid. Feeding either FO or PO lowered the content of 20:4(n - 6) in hepatic phosphatidylethanolamine, whereas clofibric acid increased it. The decrease in the level of 20:4(n - 6) in serum phospholipid was produced by feeding either FO or PO and by the administration of clofibric acid as well. There was a high correlation for the levels of 20:4(n - 6) between hepatic phosphatidylcholine and serum phospholipid. The changes brought about by dietary oils and clofibric acid in renal phosphatidylcholine was similar to those observed in liver. The content of 20:4(n - 6) in renal phosphatidylcholine was highly correlated with the level of 20:4(n - 6) in serum phospholipid. Other phospholipids in kidney responded less sensitively to the manipulation by dietary oils and clofibric acid. These results suggest that the level of 20:4(n - 6) in renal phosphatidylcholine is regulated by the level of 20:4(n - 6) in hepatic phosphatidylcholine through the changes in serum level of 20:4(n - 6). Formation of prostaglandin E2 in kidney slices was dependent on the content of 20:4(n - 6) in renal phosphatidylcholine.

Dietary manipulation by perilla oil and fish oil of hepatic lipids and its influence on peroxisomal beta-oxidation and serum lipids in rat and mouse

Rats and mice were fed a diet, prepared with soybean oil (SO), perilla oil (PO) or fish oil (FO), for 4 weeks. Compared with the groups of SO-feeding, FO-feeding increased content of eicosapentaenoic acid (20:5 n-3), docosapentaenoic acid (22:5 n-3) and docosahexaenoic acid (22:6 n-3) and PO-feeding elevated the content of alpha-linolenic acid (18:3 n-3), 20:5 n-3 and 22:5 n-3 or hepatic lipids of both rats and mice. FO-feeding increased the activity of peroxisomal beta-oxidation in the livers of both rats and mice. The activities of peroxisomal beta-oxidation in rats and mice that were fed FO diet at a high fat (40% of energy) concentration corresponded to 20% and 30%, respectively, of the maximum activities induced by peroxisome proliferators (4-chlorophenoxyisobutyric acid or perfluorooctanoic acid). To a lesser extent, PO-feeding elevated this activity too. There were significant correlations between peroxisomal beta-oxidation activity and the content of either 20:5 n-3, 22:5 n-3 or 22:6 n-3 in hepatic lipids. FO-feeding decreased effectively serum level of cholesterol of both rats and mice. The reduction in serum cholesterol by feeding PO was less pronounced than that observed with FO-feeding. A high correlation was found between 22:6 n-3 content in hepatic lipids and serum concentration of cholesterol. Although FO-feeding lowered the level of circulating triacylglycerol, PO-feeding produced no change. No substantial correlation was observed between the hepatic content of n-3 fatty acid and the concentration of serum triacylglycerol.(ABSTRACT TRUNCATED AT 250 WORDS)

Mutants of Arabidopsis deficient in the synthesis of alpha-linolenate. Biochemical and genetic characterization of the endoplasmic reticulum linoleoyl desaturase

The overall fatty compositions of leaf and root lipids from a mutant of Arabidopsis thaliana were characterized by reduced levels of linolenate (18:3) and correspondingly elevated levels of linoleate (18:2) as a consequence of a single nuclear mutation at the fad3 locus. Comparison of the fatty acid compositions of individual lipids from wild type and mutant plants showed that chloroplast lipids were largely unaffected by the mutation, whereas each of the phospholipids synthesized on the endoplasmic reticulum in the mutant exhibited a marked reduction in the proportion of 18:3 relative to wild type. These and other results indicate that the fad3 mutants are deficient in the activity of an endoplasmic reticulum 18:2 desaturase. In root tissues, this enzyme appears to account for over 80% of the 18:3 present. However, in young leaves of the mutant, phosphatidylcholine (the major phospholipid) contains 16% 18:3 compared with 29% in the wild type, and the proportion of 18:3 in this lipid increases with plant age in both wild type and mutant plants. These results reflect an exchange of lipid between the chloroplast and endoplasmic reticulum that allows the chloroplast desaturases to provide highly unsaturated lipids to the extrachloroplast membranes of leaf cells.

Combined effects of dietary protein and fat on lipid metabolism in rats

The combined effects of dietary protein (casein, whey protein, or soy protein) and fat (safflower oil, perilla seed oil, or their mixed oil; linoleic acid/alpha-linolenic acid = 5.0) on several lipid parameters were studied in rats. Serum cholesterol and triglyceride levels were lower in perilla seed oil groups irrespective of the protein sources. Liver triglyceride level, and fecal excretion of steroids were influenced mainly by protein sources, particularly isolated soy protein lowered liver triglyceride level, and increased the fecal steroid excretion. The fatty acid composition of liver phosphatidylcholine was influenced by dietary fat sources. The proportion of arachidonic acid was significantly lower in rats fed perilla seed oil than in those fed safflower oil or mixed oil, while the proportion of eicosapentaenoic acid was higher in rats fed perilla seed oil than in those fed safflower oil. Arachidonic acid/linoleic acid ratio was significantly lower in perilla seed oil groups, and tended to be higher in casein groups. Eicosapentaenoic acid/arachidonic acid ratio was influenced by both dietary protein and fat, and protein-fat interaction was observed. Eicosapentaenoic acid/arachidonic acid ratio was higher in perilla seed oil groups, and isolated soy protein in perilla seed oil groups lowered the ratio in comparison with other protein sources in perilla seed oil groups.

Dietary alpha-linolenic acid at 1.3 g/kg maintains maximal docosahexaenoic acid concentration in brain, heart and liver of adult rats

We have previously determined the dietary alpha-linolenic requirement for membrane synthesis in the developing animal. This study measures the dietary requirement for maintaining normal membrane composition in adult rats, as determined by 22:6(n-3) (docosahexaenoic acid) concentration. Sixty-day-old rats, previously fed a diet containing both linoleic and alpha-linolenic acid, were divided into nine groups, each receiving different quantities of alpha-linolenic acid but the same amount of linoleic acid. They were killed 4 wk after initiation of the new diet to determine the minimum quantity of alpha-linolenic acid required in the diet for maintaining the 22:6(n-3) tissue concentration in brain (whole tissue, myelin and nerve endings), liver and heart. The minimal amount of dietary alpha-linolenic acid that maintained the maximal 22:6(n-3) level and minimal 22:5(n-6) level in tissues was considered to be the dietary requirement. The quantity was found to be 1.30 g/kg diet (0.26% of dietary energy). It was lower than that found for the developing animal (0.4% of energy). At lower quantities of dietary alpha-linolenic acid, 22:6(n-3) was replaced by 22:5(n-6) in the organs examined, except in nervous tissue, in which 22:6(n-3) was highly preserved.

Rat vitamin E status and heart lipid peroxidation: effect of dietary alpha-linolenic acid and marine n-3 fatty acids

Three groups of sixteen male rats each were fed semi-purified diets containing 15% by weight of lipid for a period of 4 wk. The diets contained the same amount of polyunsaturated fatty acids (PUFA) (20% of total fatty acids) and saturated fatty acids (19% of total fatty acids). Dietary PUFA were represented exclusively by linoleic acid (18:2 diet), or 10% linoleic acid and 10% linolenic acid (18:3 diet), or 10% linoleic acid and 10% long-chain n-3 fatty acids (LCn-3 diet). The overall amount of vitamin E was similar in the three diets, i.e., 140, 133 and 129 mg/kg diet, respectively. Following appropriate extraction, tocopherol levels in heart, liver, brain, adipose tissue (AT) and plasma were measured by high-performance liquid chromatography. The level of vitamin E in the heart decreased with n-3 PUFA diets, most markedly with LCn-3 PUFA. Liver and AT vitamin E contents also decreased with n-3 PUFA diets when expressed as micrograms/mg total lipids and micrograms/mg phospholipids, respectively. Total plasma vitamin E was lower in rats fed the LCn-3 diet, but there was no significant difference when expressed as microgram/mg total lipids. Brain vitamin E was not affected by the various diets. In vitro cardiac lipid peroxidation was quantified by the thiobarbituric acid reactive substances (TBARS) test. Heart homogenates were incubated at 37 degrees C for 15 and 30 min in both the absence (uninduced) or presence (induced) of a free radical generating system (1 mM xanthine, 0.1 IU per mL xanthine oxidase, 0.2 mM/0.4 mM Fe/ethylenediaminetetraacetic acid). TBARS release was time-independent but significantly higher when LCn-3 fatty acids were fed to rats in either the uninduced or induced system. The study demonstrated that n-3 PUFA diets can influence vitamin E status of rats even in short-term experiments and can change the susceptibility of the heart to in vitro lipid peroxidation.

Dietary alpha-linolenic acid alters tissue fatty acid composition, but not blood lipids, lipoproteins or coagulation status in humans

We examined the effect of dietary alpha-linolenic acid (ALA) on the indices of lipid and coagulation status and on the fatty acid composition of serum and peripheral blood mononuclear cell (PBMNC) lipids in ten healthy men (age 21-37 yr) who consumed all their meals at the Western Human Nutrition Research Center for 126 d. There was a stabilization period of 14 d at the start when all 10 subjects consumed the basal diet (BD) containing 23.4 energy percent (en%) fat and two intervention periods of 56 d each. During the first intervention period, 5 subjects consumed the BD containing 23.4 en% fat, and 5 subjects consumed a diet providing 6.3% calories from alpha-linolenic acid [flaxseed oil (FSO) diet containing 28.8 en% fat]. Diets were crossed over between the two groups during the second intervention period. Feeding the FSO diet did not significantly alter serum triglycerides, cholesterol, high-density lipoproteins, low-density lipoproteins, apoprotein A-I and apoprotein B when compared to the corresponding values in the subjects fed the BD, nor was there any effect of the FSO diet on the bleeding time, prothrombin time and partial prothrombin time for these subjects. Feeding the ALA-containing diet did cause a significant increase in ALA concentration in serum (P < 0.001) and PBMNC lipids (P < 0.05). It also caused a significant increase (P < 0.05) in the eicosapentaenoic and docosapentaenoic acid contents of PBMNC lipids, and a decrease (P < 0.01) in linoleic and eicosatrienoic acid contents of serum lipids.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of age and alpha-linolenic acid deficiency on delta 6 desaturase activity and liver lipids in rats

The combined effects of age and of diet deficient in n-3 fatty acids on delta 6 desaturation of linoleic acid and on lipid fatty acid composition were studied in the liver of the rat at 2, 6, 12, 18 and 24 mon of age. The profiles of delta 6 desaturase activity and fatty acid composition were studied in the deficient rats refed, at these different ages, either with 18:3n-3 (mixture of peanut and rapeseed oils) or with 20:5n-3 + 22:6n-3 (fish oil) diets for 2, 4, 8 or 12 wk. Results showed that the liver delta 6 desaturation activity in the control rats remained high at 2 and 6 mon, decreased by 30% from 6 to 12 mon, and then remained stable from 12 to 24 mon. In the deficient rats, this activity remained high during the entire period studied. Thus, the profile of liver delta 6 desaturase activity after puberty was not related to age only; it also depended on the polyunsaturated fatty acid (PUFA) n-6 and n-3 balance in the diet. In the controls, in parallel with the delta 6 desaturase activity, PUFA metabolism could be divided into three periods: a "young" period, and "old age" period, separated by a period of transition between 6 and 12 mon. Recovery from PUFA n-3 deficiency occurred at all ages but in a different manner depending on whether the rats were "young" or "old". Recovery was faster if long-chain n-3 PUFA rather than alpha-linolenic acid were supplied in the diet.

Polyunsaturated fatty acid metabolism and acetylated low density lipoprotein uptake in J774A.1 cells

The mechanism of the antiatherogenic activity of n-3 polyunsaturated fatty acids is not well understood. In these studies, we studied the metabolism of unsaturated fatty acids in murine macrophage-like J774A.1 cells. The major metabolic pathway of 18- and 20-carbon chain unsaturated fatty acids in these cells is the sequence of 2-carbon chain elongation, successive two steps of delta 8- and delta 5-desaturation, and additional elongation. Polyunsaturated fatty acids, arachidonic acid [20:4 (n-6)] and eicosapentaenoic acid [20:5 (n-3)], are elongated into 22:4 (n-6) and 22:5 (n-3) fatty acids, respectively. Accumulation of 22:4 (n-6) and 22:5 (n-3) fatty acids shows that J774A.1 cells have an active chain elongation activity, but lack delta 4-desaturase activity. Furthermore, J774A.1 cells demonstrated almost negligible delta 6-desaturase activity. Enrichment of the membrane lipids of J774A.1 cells with polyunsaturated fatty acids, arachidonic acid [(20:4 (n-6)] and eicosapentaenoic acid [(20:5 (n-3)], increased membrane fluidity and decreased the uptake of acetylated low density lipoprotein.

High alpha-linolenic acid flaxseed (Linum usitatissimum): some nutritional properties in humans

Although high alpha-linolenic acid flaxseed (Linum usitatissimum) is one of the richest dietary sources of alpha-linolenic acid and is also a good source of soluble fibre mucilage, it is relatively unstudied in human nutrition. Healthy female volunteers consumed 50 g ground, raw flaxseed/d for 4 weeks which provided 12-13% of energy intake (24-25 g/100 g total fat). Flaxseed raised alpha-linolenic acid and long-chain n-3 fatty acids in both plasma and erythrocyte lipids, as well as raising urinary thiocyanate excretion 2.2-fold. Flaxseed also lowered serum total cholesterol by 9% and low-density-lipoprotein-cholesterol by 18%. Changes in plasma alpha-linolenic acid were equivalent when 12 g alpha-linolenic acid/d was provided as raw flaxseed flour (50 g/d) or flaxseed oil (20 g/d) suggesting high bioavailability of alpha-linolenic acid from ground flaxseed. Test meals containing 50 g carbohydrate from flaxseed or 25 g flaxseed mucilage each significantly decreased postprandial blood glucose responses by 27%. Malondialdehyde levels in muffins containing 15 g flaxseed oil or flour/kg were similar to those in wheat-flour muffins. Cyanogenic glycosides (linamarin, linustatin, neolinustatin) were highest in extracted flaxseed mucilage but were not detected in baked muffins containing 150 g flaxseed/kg. We conclude that up to 50 g high-alpha-linolenic acid flaxseed/d is palatable, safe and may be nutritionally beneficial in humans by raising n-3 fatty acids in plasma and erythrocytes and by decreasing postprandial glucose responses.

Utilization of extracellular lipids by HT29/219 cancer cells in culture

Uptake and incorporation of long-chain fatty acids were studied in a human colorectal cancer cell line (HT29/219) grown in culture medium supplemented with either fetal calf serum (FCS) or horse serum (HS). The cells were grown for 120 h with no change of medium; the two major cellular lipid classes, the phospholipids and the triacylglycerols, were analyzed at regular time-points. We observed significant changes in the concentration of most fatty acids throughout culture, and differences in their composition when different sera were used to supplement the medium. Minimal levels of free fatty acids were found in the cells, indicating a very small "free fatty acid pool". A major difference between the cells grown in media supplemented with different sera was the changes observed in concentrations of cellular polyunsaturated fatty acids during growth. In cells grown with FCS (in which 20:4n-6 is present), the levels of this acid in the phospholipid and triacylglycerol fractions declined rapidly during cell growth, suggesting further metabolism. In cells grown in medium supplemented with HS, 18:2n-6 was the major polyunsaturated acid present. There was clear evidence that this acid accumulated in the cellular triacylglycerol and phospholipid fractions. Furthermore, its concentration did not decline during growth in culture, suggesting minimal conversion to other polyunsaturated n-6 acids. Our results suggest that fatty acids from additional sources in the medium, for example triacylglycerols and phospholipids associated with the lipoproteins, are taken up by the cells. There is also indication of cellular fatty acid synthesis, particularly of monounsaturated and saturated acids during the culture period.(ABSTRACT TRUNCATED AT 250 WORDS)