Showing papers on "Lipid biosynthesis published in 1990"

Effects of propionate on lipid biosynthesis in isolated rat hepatocytes.

Abstract: The effects of propionate, a product of intestinal fiber fermentation, on fatty acid and sterol synthesis were studied in isolated rat hepatocytes. Fatty acid synthesis, as measured by tritium incorporation from 3H2O, was inhibited in the presence of 1 mmol/L propionate with no substrate additions or additions of acetate, butyrate, lactate or oleate. Incorporation of [1-14C]acetate into fatty acids was also inhibited in the presence of propionate. Although propionate markedly depressed [1-14C]acetate incorporation into sterols in hepatocyte preparations, tritium incorporation from 3H2O into sterols was not inhibited, indicating that overall sterol synthesis was not affected. Thus, in vitro, the effect of propionate on lipid metabolism is apparently limited to inhibition of de novo fatty acid synthesis.

Isolation of EMS-induced mutants in Arabidopsis altered in seed fatty acid composition.

Abstract: Mutants of Arabidopsis thaliana were identified by screening pedigreed M3 seed collections from EMS-treated plants for changes in fatty acid (FA) composition. The FA phenotypes of the most dramatic mutants are as follows: G30 and 1E5 (allelic) lack linolenic acid (18∶3) and are elevated in linoleic acid (18∶2); 4A5 is deficient in 18∶2 and 18∶3 and fourfold increased in oleic acid (18∶1); 9A1 lacks all FAs > C18 and is twofold increased in 18∶1; 1A9 is twofold increased in palmitic acid (16∶0) and decreased by one-half in 18∶1; 2A11 is two-to threefold increased in stearic acid (18∶0) and decreased by one-half in 18∶1. Based on segregation of F2 selfed plants derived from crosses to wild type, all of these phenotypes are the result of single gene mutations.

Phospholipid biosynthesis and poliovirus genome replication, two coupled phenomena.

Abstract: Poliovirus infection leads to an increase of phospholipid synthesis and the proliferation of new membranes, giving rise to a great number of cytoplasmic vesicles in the infected cells Viral RNA replication is physically associated with these newly-synthesized membranes Cerulenin, an inhibitor of lipid biosynthesis, effectively blocks the growth of poliovirus in HeLa cells The presence of cerulenin after virus entry prevents the synthesis of poliovirus proteins However, if this antibiotic is added at later stages of the virus replication cycle, it has no effect on viral translation itself, nor on the proteolytic processing and myristoylation of poliovirus proteins The synthesis of viral, but not cellular RNA is selectively inhibited by cerulenin Analysis of the viral RNA made in poliovirus-infected cells by specific minus-or plus-stranded RNA probes suggests a selective blockade by cerulenin of plus-strand RNA synthesis Finally, the synthesis of phospholipids and the proliferation of membranes does not take place if cerulenin is added to the culture medium These findings indicate that continuous phospholipid synthesis is required for efficient poliovirus genome replication and provide new insights towards the understanding of the molecular events that occur during poliovirus growth

Lipid synthesis and fatty acid composition in nannochloropsis sp. (eustigmatophyceae) grown in a light‐dark cycle1

Abstract: Chemical composition and lipid biosynthesis were studied in the marine eustigmatophyte Nannochloropsis sp. Grown under a 12:12 h light-dark regime. Cellular division occurred in the dark and was associated with a reduction in cell volume. The cellular content of chlorophyll a and carotenoids increased during the light period and decreased during the dark period. Other cellular components, such as proteins, carbohydrates and lipids, followed a similar pattern. Nannochloropsis sp. Incorporated acetate, mostly into lipids during the light period, whereas a low rate of acetate incorporation was observed during the dark period, mostly into nonlipid compounds. Neutral lipids such as triacylglycerol were synthesized and accumulated in the light and showed a rapid turnover in the dark. Polar structural lipids such as monogalactosyl diacylglycerol were synthesized during the light period and hardly turned over during the dark period. Changes in lipid content were associated with variations in cellular fatty acid composition. The light period was characterized by an increase in the percentage of C16:0 and 16:1 fatty acids associated with triacylglycerols. However, in the dark period, as triglycerides were consumed for cellular maintenance, the relative distribution of the C20:5 fatty acid associated with the galactolipids increased.

Storage-protein regulation and lipid accumulation in microspore embryos of Brassica napus L.

Abstract: Embryos derived in vitro from isolated microspores of Brassica napus L. were compared with their zygotic counterparts. Parameters investigated included storage-protein accumulation and gene expression, fattyacid composition, storage-lipid biosynthesis, and the appearance of oil-body proteins. The microspore embryos accumulate storage-protein and show increases in levels of their transcripts during the torpedo stage. These embryos were sensitive to abscisic acid (ABA) with respect to accumulation of storage-protein mRNA and oil-body proteins. Post-transcriptional regulation of cruciferin accumulation is indicated by a disparity between ABA-enhanced transcript accumulation and a less marked effect at the level of protein accumulation. To investigate storage-lipid profiles, two cultivars of Brassica napus, Reston and Topas, were used. The former accumulates major quantities of C20 (11.2%) and C22 (39.9%) fatty acids in its seeds, the latter predominantly C18 fatty acids. The higher-molecular-weight fatty acids (>C18) normally occur only in seeds and were used as biochemical markers for seed-specific metabolism in microspore embryos. Microspore embryos from Reston were found to accumulate C20 (10.6%) and C22 (31.2%) fatty acids after 35 d in culture at levels and proportions comparable to those found in seeds. Similarly, microspore embryos of Topas had a fatty-acid profile similar to that of mature Topas seed. Activities of enzymes involved in the accumulation of storage lipids (erucoyl-CoA synthetase [EC 6.2.1.3], erucoyl-CoA thioesterase [EC 3.1.2.2] and erucoyl-CoA acyltransferase [EC 2.3.1.15 or EC 2.3.1.20]) were detected in torpedostage microspore embryos. Their specific activities were higher than have been reported to date for analogous preparations from zygotic embryos of B. napus. The similarities in storage-lipid and protein composition of these embryos to their zygotic counterparts, along with their sensitivity to ABA, indicate that microspore embryos might be exploited to facilitate studies of biochemistry and gene regulation in oilseeds.

Adaptation of the Photosynthetic Apparatus to Irradiance in Dunaliella tertiolecta: A Kinetic Study.

Abstract: The time course of adaptation from a high to a low photon flux density was studied in the marine chlorophyte Dunaliella tertiolecta. A one-step transition from 700 to 70 micromole quanta per square meter per second resulted in a reduction of doubling rate from 1.1 to 0.4 per day within 24 hours, followed by a slower accumulation of photosynthetic pigments, light harvesting antenna complexes, Photosystem II reaction centers and structural lipids that constitute the thylakoid membranes. Photoregulated changes in the biochemical composition of the thylakoid proteins and lipids were functionally accompanied by decreases in the minimal photosynthetic quantum requirement and photosynthetic capacity, and an increase in the minimal turnover time for in vivo electron transport from water to CO2. Analysis of de novo synthesis of thylakoid membranes and proteins indicates that a high light to low light transition leads to a transient in carbon metabolism away from lipid biosynthesis toward the synthesis of the light harvesting antenna protein complexes, accompanied by a slower restoration rate of reaction centers and thylakoid membranes. This pattern of sequential synthesis of light harvesting complexes followed by reaction centers and membranes, appears to optimize light harvesting capabilities as cells adapt to low photon flux densities.

Dietary lipids and thrombosis. Relationships to atherosclerosis.

Abstract: A high intake of saturated fatty acids and cholesterol is associated with a high incidence of occlusive arterial lesions involving both atherosclerosis and thrombosis. The evidence is based on epidemiological, experimental, and clinical studies. Such dietary habits increase serum low density lipoprotein cholesterol, a main risk factor for atherosclerosis. The mechanisms by which dietary saturated fatty acids are connected to arterial thrombogenesis are only partly known. Experimental and epidemiological studies also indicate an association between dietary saturated fatty acids and venous thrombosis; however, the chain of evidence lacks documentation from prospective clinical studies. When unsaturated fatty acids of the (n-9), (n-6), or (n-3) families replace saturated fatty acids in the diet, risk factors related to atherosclerosis may be reduced and the development of atherosclerosis, inhibited. This potential is related both to the reduction of saturated fatty acids and, in varying degrees, to the individual unsaturated fatty acids. The very long-chain fatty acids of the (n-3) family and probably also linoleic acid of the (n-6) family have the potential to inhibit thrombogenesis. In this respect, the effect of the individual fatty acids seems even more important. To obtain an optimal dietary lipid composition for the prevention of atherosclerosis and thrombosis, it is important to appreciate the metabolic and structural effects of the individual fatty acids. The interaction between the various dietary fatty acids and their effects on lipid biosynthesis is still only partly known. The present nutritional recommendations include a low intake of saturated fatty acids and cholesterol and a balanced content of the unsaturated fatty acids and represent a well-documented approach to the prevention of both processes.

Changes in fatty acid composition of sunflower (Helianthus annuus) seeds in response to time of nitrogen application, supply rates and defoliation.

Abstract: (...) The results are difficult to interpret in termes of our current knowledge of lipid biosynthesis. N supply rates may affect the rate of hydrolysis of fatty acid complexes or their transport from the proplastid to the cytosolic compartment. There was no compelling support for the hypothesis that N supply rates before floret initiation were affecting fatty acid composition through their effects on other plant characters such as leaf mass, seed number or single seed weight

Lipid biosynthesis in seeds of mustard (Brassica juncea) influenced by zinc and sulphur deficiency

Abstract: In developing seeds of mustard (Brassica juncea L. cv. RLM 198) the period between 20 and 30 days after fertilization (DAF) was identified as the period of active lipid biosynthesis, although dry matter continued to accumulate until maturity. The period of lipid synthesis was associated with a decrease in starch, soluble sugars and protein, thus, giving rise to precursors for the biosynthesis of lipids. Besides decreasing the dry matter content (on both % and seed basis), Zn and S deficiency caused a significant (P > 0.05) reduction in oil content. As compared to control, the decrease in oil content was 11, 12 and 18% at 30 DAF and 4, 9 and 16% at maturity in Zn, S and (Zn+S) deficient treatments, respectively. Throughout the period of seed development, a significant decrease in starch and protein with a slight accumulation of soluble sugars was observed due to deficiency of Zn or S. The rate of [l-14C]-acetate incorporation into total lipids, which was maximal at 30 DAF, also displayed a significant decrease due to the abovementioned mineral deficiencies. Addition of Zn or S in vitro, enhanced the lipid synthesis at all stages of seed development. Under Zn and S deficiency, the phospholipids increased from 10 to 30 DAF and then declined until maturity. However, the proportion of glycolipids and free fatty acids increased, with a corresponding decrease in total glycerides. Further, in deficiency treatments, there was an increase in 22:1 with a corresponding decrease in 18:1, 18:2 and 18:3 in developing and mature mustard seeds.

The role of membrane lipids in drought resistance of plants

Abstract: SummaryIn greenhouse as well as field-grown plants of Vigna unguiculata and Gossypium hirsutum submitted to drought, leaf membrane lipids show a series of modifications: 1 - A decrease in polar lipid content under severe water stress in sensitive and resistant varieties, due essentially to a decrease in monogalactosyl-diacylglycerol (MGDG) content.2 - A decrease in the degree of unsaturation of fatty acid in sensitive varieties, due to a degradation of linolenic acid (18:3).These modifications result from a slowing down of lipid biosynthesis and from an acceleration of degradative enzymatic processes.Comparison between lipid and fatty acid compositions of drought-susceptible and drought-tolerant varieties from various plant species, suggest that the linolenic acid content of the leaf membranes is related to a lack of ability of cells to withstand low water potentials. Clearly, plants having a low linolenic acid content from MGDG are more resistant than the others. This may be related to the susceptibility...

Adaptation to temperature: phospholipid synthesis in hepatocytes of rainbow trout

Abstract: De novo phospholipid biosynthesis was assayed in isolated hepatocytes of rainbow trout (Oncorhynchus mykiss) both fully acclimated to 5 or 20 degrees C and undergoing acclimation from one temperature extreme to the other. Incorporation of [14C]choline, [3H]ethanolamine, and [3H]serine into phosphatidyl-choline (PC), phosphatidylethanolamine (PE), or both, was followed to assess metabolic capacity. PE biosynthesis rates exceeded those for PC four- to fivefold. Methylation of PE accounted for 10 (20 degrees C)-17% (5 degrees C) of the synthetic capacity for PC, whereas 6 (20 degrees C-acclimated)-27% (5 degrees C-acclimated) of PE synthesis was derived from phosphatidylserine (PS) decarboxylation. Several factors may contribute to the altered proportions of PE and PC or unsaturated molecular species of phospholipids characteristic of thermally acclimated animals. 1) Activities of choline and ethanolamine phosphotransferase pathways were significantly higher, and decarboxylation activity lower, in 20 degrees C than in 5 degrees C-acclimated trout, resulting in maintained PE synthesis despite a general depression of lipid biosynthesis at cold temperatures. 2) PC biosynthesis depended more on temperature (Q10 = 2.6-3.0) than that of PE (Q10 = 1.8-2.2), causing the ratio of PC/PE synthesis to be positively correlated with temperature. 3) Contribution of methyltransferase pathway to the synthesis of PC was higher at 5 than 20 degrees C. 4) The percentage of ethanolamine incorporation recovered in PC increased threefold in the early stages of warm acclimation. However, not all adjustments in biosynthetic capacity (most notably a 10-fold stimulation of PC synthesis 2 days after transfer of warm-acclimated trout to 5 degrees C) influence membrane lipid composition, implicating other processes in the regulation of this parameter.

Acetyl-coenzyme a carboxylase from the marine prymnesiophyte isochrysis galbana

Abstract: As the enzyme ACCase is considered as a key regulatory enzyme in lipid biosynthesis, a detailed study of its molecular properties and kinetics was performed and is reported herein

Effect of dietary carbohydrates and ethanol on expression of genes encoding sn-glycerol-3-phosphate dehydrogenase, aldolase, and phosphoglycerate kinase in Drosophila larvae.

Abstract: The genes encoding glycolytic enzymes inDrosophila form a group of functionally related genes that may be coordinately regulated and thus controlled by common factors. We have examined the effect of dietary carbohydrates and ethanol on expression of the genes encoding glycerol-3-phosphate dehydrogenase (GPDH), aldolase (ALD), and phosphoglycerate kinase (PGK) inD. melanogaster larvae. GPDH activity and transcript abundance increased in response to ethanol and additional amounts of several different carbohydrates. In addition, the levels of two alternatively processedGpdh transcripts were differentially regulated by the treatments. The nutritional conditions tested had little or no effect on the activities and transcript levels of ALD and PGK. These results indicate that changes in dietary conditions affect expression of specific genes and do not evoke a general response from genes involved in cellular metabolism. The observation that dietary carbohydrates and ethanol increaseGpdh expression without affecting expression ofAld andPgk reinforces previous suggestions that dietary carbon can be diverted by GPDH from glycolytic catabolism into lipid biosynthesis.

Lipid metabolism of Pleurotus sajor caju.

Abstract: Summary The biosynthesis of lipids in the mycelium and sporophore of Pleurotus sajor caju was studied. Whereas in the mycelium the biosynthesis of lipids was directly primarily towards storage (e.g. tri-acylglycerols), in the sporophore it was directed towards structural components (e.g. sterols). The incorporation of 14C precursors into non-polar and polar lipid fractions was generally similar for 14C acetate, 14C palmitate, 14C oleate and 14C linoleate in the case of mycelium and sporophore. It appears that linoleic acid was utilised as a source of acetate for lipid biosynthesis in the sporophore. A significantly higher incorporation of label was seen in sporophore sterol than in mycelial sterol. Malate dehydrogenase activity increased in the mycelium grown in the presence of lipids. Lipase of P. sajor caju was inducive. The growth of P. sajor caju was enhanced by increased lipid utilisation. The implications of these results on commercial cultivation of this fungus are discussed.

Acetyl coenzyme A carboxylase in species of Triticum of different ploidy.

Abstract: The cellular amounts and cellular activities of acetyl CoA carboxylase (ACC; EC 6.4.1.2.) were determined in the first leaves of diploid, tetraploid and hexaploid species of Triticum (wheat). Per leaf the ACC activities were very similar in T. monococcum (2 χ), T. dicoccum (4 χ) and T. aestivum (6 χ). The ACC activity per chloroplast also showed little variation between species of different ploidy but since chloroplast number increases with ploidy, the ACC activities and ACC amounts per cell also increased with ploidy. These cellular increases in ACC amounts associated with increases in gene dosage were highly co-ordinated in the diploids T. monococcum and T. tauschii and their respective autotetraploids so the specific activity of ACC was highly conserved in these plants. The relevance of these findings to attempts to genetically manipulate lipid biosynthesis in chloroplasts is discussed.

Lipid biosynthesis in adult Acyrthosiphon pisum: effect of age and symbiont population.

Abstract: The incorporation of [1-14C]acetate into total lipids in 1-day-old adult pea aphids is 3.3-fold higher than in 20-, 22-, and 24-day old adults. The polar lipid fraction was the main lipid class synthesized at any age and contained primarily eighteen carbon fatty acids. While the relative mass of 18:0, 18:1 and 18:2 decreased in older aphids, the relative amount of label incorporated into these fatty acids remained constant. Myristic acid was the main fatty acid of the triacylglycerol fraction, and the relative amount of radioactivity incorporated into this fatty acid decreased in older aphids. Twenty-day-old aphids had 60% fewer mycetocytes than did 1-day-old insects. We conclude that symbionts within the mycetocytes do not appear to be involved in the synthesis of linoleic acid, while their role in the synthesis of myristic acid is less clear.

Biochemistry and Endocrine Regulation of Sex Pheromone Production in the Housefly and German Cockroach

Abstract: There has been a dramatic increase of interest in the biosynthesis of insect sex pheromones over the last decade (Prestwich and Blomquist, 1987). It now appears that many of the rather novel compounds that are components of insect sex pheromones are produced by the addition of a few ancillary enzymes to those of “normal” metabolism. For example, the carbon skeletons of many lepidopteran sex pheromones are produced from common fatty acids by a novel delta-ll desaturase and highly specific chain-shortening reactions (Bjostad et al., 1987). In the Coleoptera, sex pheromones are often produced by the use of one or two highly specific enzymes that convert dietary material, usually isopreniod, to active pheromones (Vanderwel and Oehlschlager, 1987). By using one or a few ancillary enzymes to alter the products of the usual lipid metabolic pathways or to alter dietary constituents, the insect requires much less genetic material than would be necessary to code for a complete set of enzymes that would be expressed only in the pheromone-producing tissue. This phenomenon appears to exist in the housefly, Musca domestica, and the German cockroach, Blattella germanica, as hormone control of several enzymes could account for alteration of the products of cuticular lipid biosynthesis to produce the female-specific sex pheromone components.

Lipid biosynthesis in Paramphistomum microbothrium (Trematoda).

Abstract: In vitro studies with Paramphistomum microbothrium indicated that the trematode is capable of synthesizing its complex lipids using exogenous substrates. U-14C glucose and 2-14C acetate were predominantly incorporated into phospholipids while 1-14C oleic acid and U-14C palmitic acid appeared more in the neutral lipids. A large proportion of the labelled acetic acid incorporated into neutral lipids appeared in the triglycerides. P. microbothrium is capable of synthesizing its cholesterol de novo.

Mechanisms of hyperbaric-oxygen inhibition of growth and net biosynthesis of RNA, DNA, protein and lipids in Escherichia coli.

Abstract: The effects of hyperbaric oxygen at 4.2 atmospheres on growth, induction of stringency and net synthesis of RNA, DNA, protein and lipid by Escherichia coli were evaluated by measuring culture absorbance and incorporation of specific 14C-labelled substrates. Combinations of different bacterial strains, various nutritional conditions and chloramphenicol were used to suppress or allow induction of stringency and to mitigate or enhance other consequences of reported sites of oxygen toxicity. In minimal medium with glucose as the sole organic nutrient, there was almost instantaneous inhibition of net biosynthesis of four major macromolecular constituents: lipid, RNA, DNA and protein. Net lipid biosynthesis primarily failed indirectly due to induction of stringency. Protein net synthesis declined due to induction of stringency and lack of amino acids. RNA net biosynthesis stopped from a direct effect and indirectly via induction of stringency. Net DNA biosynthesis was indirectly primarily impaired.

The effect of adrenocorticotropic hormone (ACTH) and cycloheximide (CHM) on lipid biosynthesis in the rat lung

Abstract: The influence of ACTH, CHM and of ACTH + CHM was studied on lipid metabolism of lungs of rats by usage of a radioactive precursor 14C-acetate. It was established that the biosynthesis of total lipids, of triacylglycerols as well as of free fatty acids was increased under the influence of ACTH and CHM as this effect was mostly manifested after combined action of ACTH and CHM. The investigated factors manifested inhibiting effect on the synthesis of free cholesterol and total phospholipids. ACTH stimulated incorporation of 14C-acetate in the glycerol part of triacylglycerols as well as of the total phospholipids, while CHM and the combination of CHM and ACTH had inhibiting effect on the biosynthesis of the glycerol part of triacylglycerols and of total phospholipids.