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PubMed1990

Biosynthesis of triacylglycerols containing very long chain monounsaturated acyl moieties in developing seeds.

Particulate (15,000g) fractions from developing seeds of honesty (Lunaria annua L.) and mustard (Sinapis alba L.) synthesize radioactive very long chain monounsaturated fatty acids (gadoleic, erucic, and nervonic) from [1-(14)C]oleoyl-CoA and malonyl-CoA or from oleoyl-CoA and [2-(14)C]malonyl-CoA. The very long chain monounsaturated fatty acids are rapidly channeled to triacylglycerois and other acyl lipids without intermediate accumulation of their CoA thioesters. When [1-(14)C]oleoyl-CoA is used as the radioactive substrate, phosphatidylcholines and other phospholipids are most extensively radiolabeled by oleoyl moieties rather than by very long chain monounsaturated acyl moieties. When [2-(14)C]malonyl-CoA is used as the radioactive substrate, no radioactive oleic acid is formed and the newly synthesized very long chain monounsaturated fatty acids are extensively incorporated into phosphatidylcholines and other phospholipids as well as triacylglycerols. The pattern of labeling of the key intermediates of the Kennedy pathway, e.g. lysophosphatidic acids, phosphatidic acids, and diacylglycerols by the newly synthesized very long chain monounsaturated fatty acids is consistent with the operation of this pathway in the biosynthesis of triacylglycerols.

Journal Article↗
PubMed1991

Metabolism of linolenic acid and docosahexaenoic acid in rat retinas and rod outer segments.

Docosahexaenoic acid (22:6 omega 3) is uniquely enriched in photoreceptor outer segment phospholipids, comprising up to one-half of the fatty acids of phosphatidylethanolamine and phosphatidylserine. The current study was designed to investigate the incorporation of 22:6 omega 3 into outer segment phospholipids over 12 days and to determine whether the retina contained the enzymes necessary for elongation and desaturation of the major dietary precursor of 22:6 omega 3, the essential fatty acid linolenic acid (18:3 omega 3). Sprague-Dawley rats were injected intravitreally with [14C]22:6 omega 3 or [14C]18:3 omega 3 and kept in cyclic light (12 hr light/12 hr dark) for 2 hr to 12 days. Phospholipids from rod outer segments and the remaining retinal debris were separated by two-dimensional thin-layer chromatography. [14C]22:6 omega 3 radioactivity was initially highest in phosphatidylcholine and rapidly decreased from 45% of total phospholipid labeling at 2 hr to 26% by 1 and 3 days in ROS, while phosphatidylethanolamine labeling increased from 49 to 68% by 3 days and phosphatidylserine labeling increased from 3 to 14% over 12 days. Phenacyl derivatives of total fatty acids were separated by HPLC. A substantial conversion of [14C]18:3 to [14C]20:5, [14C]22:5 and [14C]22:6 was noted after 1 days, with increasing conversion to [14C]22:6 over the 12-day period. When only one eye was injected with [14C]18:3 omega 3, negligible radioactive fatty acids were detected in the contralateral eye from 1 to 12 days post-injection demonstrating that conversion of 18:3 to 22:6 occurred primarily within the injected eye. All enzymes for elongation and desaturation of 18:3 to 22:6 appear to be present in the eye. However, the conversion of 22:5 to 22:6 by delta-4 desaturase is evidently rate-limiting and may affect phospholipid replacement during photoreceptor outer segment renewal if this pathway proves to be essential for the supply of 22:6 during disk membrane formation.

Animals↗
PubMed1988

Fatty acid specificity for the synthesis of triacylglycerol and phosphatidylcholine and for the secretion of very-low-density lipoproteins and lysophosphatidylcholine by cultures of rat hepatocytes.

1. The synthesis and secretion of glycerolipids by monolayer cultures of rat hepatocytes was measured by using radioactive choline, glycerol and fatty acids and by measuring the concentration of triacylglycerols in the cells. 2. The incorporation of glycerol into triacylglycerol and the accumulation of this lipid in hepatocytes showed little specificity for fatty acids, except for eicosapentaenoate, which stimulated least. Oleate was more effective at stimulating triacylglycerol secretion than were palmitate, stearate, arachidonate and eicosapentaenoate. 3. Linoleate, linolenate, arachidonate and eicosapentaenoate stimulated the incorporation of glycerol and choline into phosphatidylcholine that was secreted into the medium. By contrast, palmitate and stearate produced relatively high incorporations into the phosphatidylcholine that remained in the cells. 4. The incorporation of glycerol and choline into lysophosphatidylcholine in the medium was stimulated 2-3-fold by all of the unsaturated fatty acids tested, whereas palmitate and stearate failed to stimulate if the acids were added separately. When 1 mM-stearate was added with 1 mM-linoleate, the incorporation of linoleate into lysophosphatidylcholine was about 4 times higher than that of stearate. 5. It is proposed that the secretion of lysophosphatidylcholine by the liver could provide a transport system for choline and essential unsaturated fatty acids to other organs.

Animals↗
PubMed1998

MgATP has different inhibitory effects on the use of 1-acyl-lysophosphatidylcholine and lyso platelet-activating factor acceptors by neuronal nuclear acetyltransferase activities.

The inhibitory effects of MgATP on neuronal nuclear acetyltransferase activities were studied using lyso platelet-activating factor (lyso-PAF, 1-alkyl-sn-glycero-3-phosphocholine) and lysophosphatidylcholine (lyso-PC, 1-acyl-sn-glycero-3-phosphocholine). The nuclear (N1) acetylation of lyso-PC was more profoundly inhibited by MgATP. MgATP did not alter the apparent Km for acetyl-CoA in either acetylation reaction. The inhibitory effects of MgATP were not seen for other nucleotides or MgAMP-PCP. Kinase inhibitors such as staurosporine (1 microM), chelerythrine, and R59022 (diglyceride kinase inhibitor I) did not block the MgATP inhibition of either acetylation. However, the addition of phospholipids to the assays indicated a selective inhibitory effect for PIP (25-50 microM) in the nuclear acetylation of lyso-PAF. When N1 was incubated with [gamma-33P]ATP, phosphatidic acid and PIP were the principal radioactive lipid products. While the extent of MgATP inhibition of lyso-PAF acetylation was similar at different concentrations of lyso-PAF, increasing lyso-PC concentrations greatly decreased the MgATP inhibition seen in lyso-PC acetylations. Nuclear envelopes prepared in the presence of PMSF, and fraction N1 exposed to PMSF, did not show the inhibitory effect of MgATP on lyso-PC acetylation. PMSF (an inhibitor of certain phospholipase and lysophospholipase activities) did not reduce the MgATP inhibition of lyso-PAF acetylation. Arachidonoyl trifluoromethylketone, an inhibitor of cytosolic phospholipases A2 and of lysophospholipase activity associated with cPLA2, also blocked the inhibitory effect of MgATP on lyso-PC acetylation. Using radioactive lyso-PC substrate, fraction N1 produced labeled free fatty acid and phosphatidylcholine. In the presence of acetyl-CoA, the production of radioactive phosphatidylcholine increased almost 6-fold when MgATP was also included in these incubations. In the presence of MgATP and acetyl-CoA, PMSF reduced the levels of radioactive free fatty acid and phosphatidylcholine derived from lyso-PC, while Triacsin C, an inhibitor of acyl CoA synthetase, decreased phosphatidylcholine labeling. These findings suggest that MgATP inhibition of lyso-PC acetylation results from a loss of lyso-PC substrate that is largely mediated by nuclear lysophospholipase, acyl-CoA synthetase and lyso-PC acylation. Thus the neuronal nuclear production of Acyl PAF may be regulated by paths that compete for the lyso-PC substrate. In contrast, the acetylation of lyso-PAF is inhibited by PIP, a product of nuclear PI kinase reactions.

Acetyl Coenzyme A↗
PubMed1978

Distribution of radioactivity in myelin lipids following subcutaneous injection of [14C]stearate.

Blood fatty acids are an important parameter for the synthesis of brain myelin as exogenous stearic acid is needed: after subcutaneous injection to 18-day-old mice this labelled stearic acid is transported into brain myelin and incorporated into its lipids. However the acid is partly metabolized in the brain by elongation (thus providing very long chain fatty acids, mainly lignoceric acid) or by degradation to acetate units (utilized for synthesis of medium chain fatty acids as palmitic acid, and cholesterol). These metabolites are further incorporated into myelin lipids. The myelin lipid radioactivity increases up to 3 days; most of the activity is found in phospholipids; their fatty acids are labelled in saturated as well as in polyunsaturated homologues but sphingolipids, especially cerebrosides, contain also large amounts of radioactivity (which is mainly found in very long chain fatty acids, almost all in lignoceric acid). The occurrence of unesterified fatty acids must be pointed out, these molecules unlike other lipids, are found in constant amount (expressed in radioactivity per mg myelin lipid).

Animals↗
PubMed1979

The effect of essential fatty acid deprivation on the metabolic transformations of [1(-14)C]linolenate in developing rat brain.

Linolenic acid undergoes rapid metabolism in the brain of 21-day-old rats. Radioactivity is rapidly transferred from linolenic acid to the C20 (n--3) fatty acids while that in docosapentaenoic acid (22 : 5 n--3) and docosahexaenoic acid (22 : 6 n--3) gradually increases. A greater proportion of the radioactivity is associated with the polyunsaturated and less with saturated and monounsaturated fatty acids in essential fatty acid-deprived rats relative to controls.

Animals↗
PubMed1968

Biosynthesis of cyclopropyl long-chain fatty acids from cyclopropanecarboxylic acid by mammalian tissues in vitro.

1. Radioactivity from cyclopropane[(14)C]carboxylic acid is incorporated into fatty acids in vitro by rat and guinea-pig adipose tissue, by rat liver slices and by the supernatant fraction of rat liver homogenate. 2. The labelled acids are different from endogenous straight-chain fatty acids, and evidence is produced that they consist of a cyclopropyl ring in the omega-position, the remainder of the chain being built up from C(2) units (not derived from cyclopropanecarboxylic acid) in the normal way via the malonate pathway. 3. It is suggested that these unnatural acids have some metabolic effect related to the hypoglycaemic action of cyclopropanecarboxylic acid.

Adipose Tissue↗
PubMed1984

Adaptation of fatty acid composition to temperature--a study on carp (Cyprinus carpio L.) liver slices.

Liver slices obtained from warm-, and cold-adapted carp were incubated in the presence of [1-14C]sodium acetate, -stearate, -linoleate, and -linolenate at various temperatures and the distribution of radioactivity among different phospholipid fatty acids was determined. Relative labelling of saturated fatty acids is reduced, while that of long chain polyunsaturated fatty acids, especially of docosahexanoate, is increased with decreasing temperatures. Liver slices of cold adapted carp produced a fatty acid population at 25 degrees C indistinguishable from that produced by warm adapted ones at the same temperature. Liver slices obtained from cold-, and warm-adapted animals start to reorganise the pattern of labelling immediately after the exposure to the opposite temperatures as evident from pulse-chase labelling experiments. Desaturation of saturated and various unsaturated fatty acids is initiated immediately after down-shift of the temperature. This cold induced increase in desaturase activity is prevented by cycloheximide in the incubation medium. It is concluded that phospholipid fatty acid composition is continuously adjusted to the temperature and is governed partly by temperature coefficient of fatty acid synthetase and partly by induction or deactivation of desaturases in cold and warm, respectively.

Acclimatization↗
PubMed1980

Comparative utilization in vivo of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose and [1-C14] palmitate in the rat.

Female rats were injected i.v. with comparable trace amounts of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose, or [1-14C] palmitate, and killed 30 min afterwards. The radioactivity remaining in plasma at that time was maximal in animals receiving [U-14C] glucose while the appearance of radioactive lipids was higher in the [U-14C] glycerol animals than in other groups receiving hydrosoluble substrates. The carcass, more than the liver, was the tissue where the greatest proportion of radioactivity was recovered, while the greatest percentage of radioactivity appeared in the liver in the form of lipids. The values of total radioactivity found in different tissues were very similar when using either labelled glucose or glycerol but the amount recovered as lipids was much greater in the latter. The maximal proportion of radioactive lipids appeared in the fatty-acid form in the liver, carcass, and lumbar fat pads when using [U-14C] glycerol as a hydrosoluble substrate, and the highest lipidic fraction appeared in adipose tissue as labelled, esterified fatty acids. In the spleen, heart, and kidney, most of the lipidic radioactivity from any of the hydrosoluble substrates appeared as glyceride glycerol. The highest proportion of radioactivity from [1-14C] palmitate appeared in the esterified fatty acid in adipose tissue, being followed in decreasing proportion by the heart, carcass, liver, kidney, and spleen. Thus at least in part, both labelled glucose and glycerol are used throughout different routes for their conversion in vivo to lipids. A certain proportion of glycerol is directly utilized by adipose tissue. The fatty acids esterification ability differs among the tissues and does not correspond directly with the reported activities of glycerokinase, suggesting that the alpha-glycerophosphate for esterification comes mainly from glucose and not from glycerol.

Animals↗
PubMed1991

Myristic acid utilization and processing in BC3H1 muscle cells.

Because myristic acid (14:0) is important in regulating cell function, we have studied its utilization in BC3H1 muscle cells. Phosphatidylcholine contained 70-80% of the [9,10-3H]14:0 radioactivity incorporated into the cell phospholipids. In both myoblasts and myocytes, however, large amounts of radioactivity also accumulated in a labile neutral lipid pool consisting mostly of triacylglycerol. Therefore, radioactive lipid products formed when BC3H1 cells labeled with 14:0 are stimulated are not necessarily derived only from phosphatidylcholine. Elongation of [9,10-3H]14:0 occurred rapidly in the myoblasts and myocytes, and extensive desaturation also occurred in the myoblasts. Thus, even after short periods of labeling, substantial amounts of radioactivity are contained in fatty acids other than 14:0. The labeling of proteins with [9,10-3H]myristic acid was generally similar in the myoblasts and myocytes. A number of lipid-soluble, polar radioactive metabolites were released into the medium during incubation of [9,10-3H]14:0 with the cells. [1-14C] 14:0 was not converted to these compounds, indicating that they are chain-shortened 14:0 derivatives. Based on chemical analysis, two of the major products appear to be hydroxylated fatty acids. This oxidation process shows some specificity for 14:0 because similar compounds were not produced from palmitic, oleic, or linoleic acids. The myocytes formed larger amounts of the metabolites than the myoblasts, suggesting that differentiation may increase the activity of this 14:0 oxidative pathway.

Acylation↗
PubMed1985

Ia-associated invariant chain is fatty acylated before addition of sialic acid.

The murine invariant chain (Ii) was found to incorporate radioactive palmitic acid. This binding of fatty acid inhibits the formation of interchain S-S bonds, probably because the cysteine residue in the transmembrane region of the Ii chain is palmitylated. The inhibition of fatty acylation by cerulenin blocks further posttranslational maturation of the invariant chain as shown by two-dimensional gel electrophoresis of Ii immunoprecipitates. In particular, the addition of sialic acid residues is blocked. Thus, it appears that fatty acylation is essential for carbohydrate processing of the Ii chain.

Acylation↗
PubMed1975

Fat metabolism in higher plants. Production of short- and medium-chain acyl-acyl carrier protein by spinach stroma preparations treated with cerulenin.

Incubation of stroma preparations from spinach chloroplasts with low concentrations of cerulenin (10 muM) resulted in severe inhibition of fatty acid synthesis but stimulated the release of medium-chain acids in very high proportions (60-70%). Preincubation of these preparations with cerulenin in the absence of substrate exerted no additional effect on subsequent fatty acid synthesis (as measured by incorporation of [14C]acetate into fatty acids) or the pattern of radioactive acids obtained. Acyl-protein, acyl-CoA, free fatty acids and lipids were resolved from each other and analysed for their distribution of 14C-labelled fatty acids. Acyl-protein derived from cerulenin-treated preparations was the only fraction which contained short- and medium-chain acids (C6--C12). The other fractions from both control and cerulenin-treated groups consisted exclusively of C16 and C18 acids. Acyl-protein was purified by gel filtration chromatography and was characterized as acyl-acyl carrier protein.

Antifungal Agents↗
PubMed1993

Acylated proteins in Borrelia hermsii, Borrelia parkeri, Borrelia anserina, and Borrelia coriaceae.

Borrelia hermsii, Borrelia parkeri, Borrelia anserina, and Borrelia coriaceae produced several lipoproteins identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography of bacteria grown in [3H]palmitate. Five major acylated proteins were demonstrated by sequential alkaline and acid hydrolysis. High-pressure liquid chromatography of isolated proteins confirmed that covalently bound radioactivity was represented by fatty acids.

Acylation↗
PubMed1983

Role of triglycerides in endothelial cell arachidonic acid metabolism.

Arachidonic acid was incorporated into triglycerides by cultured bovine endothelial cells in a time- and concentration-dependent manner. At 75 microM or higher, more arachidonic acid was incorporated into triglycerides than into phospholipids. The triglyceride content of the cells increased as much as 5.5-fold, cytoplasmic inclusions appeared, and arachidonic acid comprised 22% of the triglyceride fatty acids. Triglyceride turnover occurred during subsequent maintenance culture; there was a 60% decrease in the radioactive arachidonic acid contained in triglycerides and a 40% decrease in triglyceride content in 6 hr. Most of the radioactivity was released into the medium as free fatty acid. The turnover of arachidonic acid, but not oleic acid in cellular triglycerides, decreased when supplemental fatty acid was added to the maintenance medium. Incorporation and turnover of radioactive arachidonic acid in triglycerides also was observed in human skin fibroblasts, 3T3-L1 cells, and MDCK cells. Other fatty acids were incorporated into triglycerides by the endothelial cells; the amounts after a 16-hr incubation with 50 microM fatty acid were 20:3 greater than 20:4 greater than 18:1 greater than 18:2 greater than 22:6 greater than 16:0 greater than 20:5. These findings indicate that triglyceride formation and turnover can play a role in the fatty acid metabolism of endothelial cells and that arachidonic acid can be stored in endothelial cell triglycerides.

Animals↗
PubMed1991

Vasopressin stimulates the mobilization and metabolism of triacylglycerol in perfused rabbit hearts.

Vasopressin stimulates several metabolic processes, including glycogenolysis, gluconeogenesis, and fatty acid oxidation, and promotes lipolysis in rabbit and hamster suprarenal adipose tissue. This study was conducted to determine whether arginine vasopressin (AVP) stimulates the metabolism of triacylglycerols in the isolated perfused rabbit heart. Since the basal output of glycerol in the rabbit heart is very low, the triacylglycerol pool was labeled with [3H]triolein, and triacylglycerol metabolism was followed by analysis of the radioactive products in the perfusate. Administration of AVP (100 ng, 92 pmol) produced a 10-fold increase in the perfusate radioactivity associated with free fatty acids and mono- and diglycerides, as well as an 8-fold increase in the effluent radioactivity associated with triacylglycerol. The V1-receptor antagonist d[(CH2)5Tyr(Me)]AVP blocked the AVP-induced increase in the output of radioactivity in a dose-related manner. The V2-receptor agonist desmopressin (DDAVP) did not increase the outflow of radioactivity. Likewise, AVP-induced release of radioactivity was inhibited when Ca2+ was omitted from the perfusion buffer. Analysis of total lipid extracts of hearts labeled with [3H]triolein showed that the residual radioactivity was associated almost exclusively with authentic triolein both before and after AVP treatment. These data suggest that AVP promotes triacylglycerol mobilization and utilization and that these processes are Ca2+ dependent and mediated by the V1-receptor. Since free fatty acids derived from triacylglycerols are the preferred metabolic substrate for the heart and since plasma AVP levels increase in cardiac stress states such as shock, these findings suggest a metabolic function of AVP in cardiovascular stress states.

Animals↗