1-acylglycerophosphate Acyltransferase Research Articles

A highly toxic coplanar polychlorinated biphenyl compound suppresses Delta5 and Delta6 desaturase activities which play key roles in arachidonic acid synthesis in rat liver.

The effect of 3,3',4,4',5-pentachlorobiphenyl (PenCB) on the synthesis of unsaturated fatty acids was studied in male Wistar rats. The arachidonic acid (20:4) content in the total lipids of liver homogenates was significantly reduced on day 5 of PenCB administration, while those of linoleic acid (18:2) and bishomo-gamma-linolenic acid (20:3) were increased. These changes in the total lipids of liver homogenates were observed following doses of PenCB ranging from 0.5 to 25 mg/kg of body weight. The same changes in these fatty acids were seen with four subtypes of microsomal glycerophospholipids in the liver. The marked reduction in the molar ratio of 20:4 to 18:2 in the lipids suggests alteration of the activity of the enzymes responsible for the synthesis of unsaturated fatty acids. The activity of Delta5 and Delta6 desaturases (arachidonic acid synthetase) in the liver microsomes was 17 and 13% of that of pair-fed control animals, whereas the activity of 1-acylglycerophosphorylcholine or 1-acylglycerophosphate acyltransferase, which transfers 20:4 or 18:2 to phospholipids, was not affected by the treatment. Thus, the reduction in the level of 20:4 that was observed can be explained by a reduction in desaturase activity. These results are evidence that the coplanar PenCB has a significant effect on the reduced synthesis of physiologically essential long-chain unsaturated fatty acids.

Comparison of phospholipid synthesis in rat salivary glands: Properties of 1-acylglycerophosphorylcholine and 1-acylglycerophosphate acyltransferase systems in microsomes

1. 1. 1-Acyl- sn-glycerol-3-phosphorylcholine and 1-acyl- sn-glycerol-3-phosphate acyltransferase activities were characterized in rat salivary gland microsomes. 2. 2. The acyl-CoA selectivities between these two kinds of lysophospholipid acyltransferase activities were very different. 3. 3. When the three major glands were compared (parotid, submandibular, sublingual), they showed their own particular acyltransferase activity, but they had very similar in acyl-CoA selectivity. 4. 4. Those observations were also compared in rat liver microsomes.

Alterations by peroxisome proliferators of acyl composition of hepatic phosphatidylcholine in rats, mice and guinea-pigs. Role of stearoyl-CoA desaturase.

Rats, mice and guinea-pigs were administered p-chlorophenoxyisobutyric acid (clofibric acid) or 2,2'-(decamethylenedithio)diethanol (tiadenol). The treatments of rats and mice with either clofibric acid or tiadenol increased markedly the activities of stearoyl-CoA desaturase, palmitoyl-CoA chain elongation, 1-acylglycerophosphate (1-acyl-GP) acyltransferase and 1-acylglycerophosphocholine (1-acyl-GPC) acyltransferase, but not 2-acylglycerophosphocholine (2-acyl-GPC) acyltransferase in liver microsomes. The treatment of guinea-pigs with clofibric acid did not cause any change in the activities of these enzymes. The treatment of guinea-pigs with tiadenol caused a slight, but significant, increase in the activities of 1-acyl-GP acyltransferase and 1-acyl-GPC acyltransferase. The treatment of rats and mice with either clofibric acid or tiadenol increased markedly the proportion of 18:1 and decreased greatly the proportion of 18:0 in liver microsomal phosphatidylcholine. However, there is a considerable difference in the effects of the two peroxisome proliferators on the composition of polyunsaturated fatty acids in phosphatidylcholine between rats and mice. The treatment of guinea-pigs with either of the two peroxisome proliferators caused no change in acyl composition of phosphatidylcholine. The possible role of stearoyl-CoA desaturation in the regulation of acyl composition of phosphatidylcholine was discussed.

Modification by clofibric acid of acyl composition of glycerolipids in rat liver: Possible involvement of fatty acid chain elongation and desaturation

Administration of p-chlorophenoxyisobutyric acid (clofibric acid) to rats induced a marked change in acyl composition of hepatic glycerolipids; a considerable increase in the proportion of octadecenoic acid (18:1) was accompanied by a marked decrease in the proportion of octadecadienoic acid (18:2). Among the glycerolipids, the changes in the proportions of 18:1 and 18:2 were the most marked in phosphatidylcholine. The change in the acyl composition of phosphatidylcholine paralleled the change in free fatty acid composition in microsomes. The treatment of rats with clofibric acid resulted in a 2.3-fold increase in activity of microsomal palmitoyl-CoA chain elongation and a 4.8-fold increase in activity of stearoyl-CoA desaturation. The activities of acyl-CoA synthetase, 1-acylglycerophosphate acyltransferase and 1-acylgly-cerophosphorylcholine acyltransferase in hepatic microsomes were increased approx. 3-, 1.7- and 3.6-times, respectively, by the treatment of rats with clofibric acid. These findings are discussed with respect to the role of fatty acid modification systems in the regulation of acyl composition of phosphatidylcholine.

Properties of acyl-coenzyme A:1-acylglycerophosphate acyltransferase and lipases in porcine erythrocyte membranes.

Acyl-CoA:1-acylglycerophosphate acyltransferase activity was found in porcine erythrocyte membranes. However, the membrane preparations did not catalyze the acylation of either 2-acylglycerophosphate or 2-acylglycerophosphocholine. The 1-acylglycerophosphate acyltransferase and the known acyl-CoA:1-acylglycerophosphocholine acyltransferase systems differ in their specificities for acyl-CoAs and in their stabilities to detergents. Diacylglycerol lipase and monoacylglycerol lipase activities were also detected in porcine erythrocytes. These two activities appear to be catalyzed by different enzymes inasmuch as diacylglycerol lipase but not monoacylglycerol lipase was completely inhibited by divalent cations. The diacylglycerol lipase was relatively specific for the 1-position yielding 2-acylglycerol. The monoacylglycerol lipase hydrolyzed 1-acylglycerol and 2-acylglycerol at comparable rates. Phosphatidic acid was dephosphorylated to form 1,2-diacylglycerol but the acyl groups of phosphatidate were not hydrolyzed significantly by the erythrocyte membranes. Thus, the origin of 1-acylglycerophosphate, a substrate for the newly described enzyme, acyl-CoA:1-acylglycerophosphate acyltransferase, in mature erythrocyte could not be ascribed to action of diacylglycerol lipase, glycerophosphate acyltransferase, or phosphatidate-specific phospholipase A. 1-Acylglycerophosphate may be supplied extracellularly or the 1-acylglycerophosphate acyltransferase activity in erythrocytes may be a remnant of de novo phosphatidate synthesizing system of reticulocytes.

Acyl coenzyme A: Phospholipid acyltransferases in porcine platelets discriminate between ω-3 and ω-6 unsaturated fatty acids

The properties of porcine platelet acyltransferases which catalyze the incorporation of unsaturated fatty acids into the 2 positions of phospholipids were compared with those of porcine liver microsomes and rat liver microsomes. There were significant differences in the relative rates of incorporation of acyl groups into phospholipids as catalyzed by the membranes from different species and organs. The 1-acylglycerophosphate acyltransferase system showed relatively broad specificity for saturated and unsaturated fatty acids, with 14- to 20-carbon chains, while unsaturated acyl-CoAs with 18- and 20-carbon chains were generally good substrates in the acylations of 1-acylglycerophosphocholine and 1-acylglycerophosphoinositol. ω-3 and ω-6 unsaturated fatty acids were recognized differently by different acyltransferase systems in platelets. When activities for combinations of ω-3 and ω-6 unsaturated acyl-CoAs with the same number of carbons and with similar number of double bonds were compared, ω-6 fatty acids were relatively more preferred substrates than ω-3 fatty acids for the 1-acylglycerophosphoinositol acyltransferase system as compared with 1-acylglycerophosphocholine acyltransferase system.

Facilitated utilization of endogenously synthesized lysophosphatidic acid by 1-acylglycerophosphate acyltransferase from Escherichia coli

Complete separation of glycerophosphate acyltransferase and 1-acylglycerophosphate acyltransferase from Escherichia coli was obtained by sequential extraction with Triton X-100. Solubilized glycerophosphate acyltransferase was reconstituted by the cholate dispersion and gel filtration method in small unilamellar vesicles. 1-Acylglycerophosphate acyltransferase could not be solubilized from the membranes and was used in endogenous membrane fragments after detergent removal. Mixing of the two preparations and subsequent incubation in the presence of glycerol 3-phosphate, palmitoyl-CoA and oleoyl-CoA resulted in the efficient synthesis of phosphatidic acid. Inclusion of exogenous lysophosphatitic acid in the assay medium resulted in a dilution of the newly synthesized lysophosphatidate. By contrast, the synthesis of phosphatidic acid from glycerol 3-phosphate by the acyltransferases present in native membrane vesicles was barely influenced by the presence of exogenous lysophosphatidic acid. When comparing the utilization of membrane-associated 14C-labeled and newly generated 3H-labeled lysophosphatidic acid, the latter appeared to be the preferred substrate. These results indicate that lysophosphatidic acid, synthesized by glycerophosphate acyltransferase, is utilized by 1-acylglycerophosphate acyltransferase without prior mixing with the total membrane-associated pool of lysophosphatidic acid, and suggest a close proximity of the two enzymes in native E. coli membranes. This property of the acyltransferases is lost upon separation and reconstitution of enzyme activities.

61] Glycerolipid acyltransferases from rat liver: 1-acylglycerophosphate acyltransferase, 1-acylglycerophosphorylcholine acyltransferase, and diacylglycerol acyltransferase: EC 2.3.1.51 acyl-CoA: 1-acyl- sn-glycerol-3-phosphate O-acyltransferase EC 2.3.1.23 acyl-CoA: 1-acyl- sn-glycero-3-phosphocholine O-acyltransferase EC 2.3.1.20 acyl-CoA: 1,2-diacyl- sn-glycerol O-acyltransferase

61] Glycerolipid acyltransferases from rat liver: 1-acylglycerophosphate acyltransferase, 1-acylglycerophosphorylcholine acyltransferase, and diacylglycerol acyltransferase: EC 2.3.1.51 acyl-CoA: 1-acyl- sn-glycerol-3-phosphate O-acyltransferase EC 2.3.1.23 acyl-CoA: 1-acyl- sn-glycero-3-phosphocholine O-acyltransferase EC 2.3.1.20 acyl-CoA: 1,2-diacyl- sn-glycerol O-acyltransferase

Possible involvement of acyltransferase systems in the formation of pulmonary surfactant lipid in rat

Dithiobis (2-nitrobenzoic acid)-resistant and -sensitive glycerophosphate acyltransferase systems were present in rat lung as in liver. The former was specific for palmitate while the latter could incorporate saturated and unsaturated acyl-CoAs comparably. The former has higher affinity for palmitate than the latter indicating that the 1-position of glycerophosphate can be acylated selectively with palmitate under certain conditions. The specificities of 1-acylglycerophosphate and 1-acylglycerophosphocholine acyltransferase systems were similar in lung and liver; both systems showed higher specificities for unsaturated acyl-CoAs. However, the selectivities observed at lower concentrations of phospholipid acceptors in the presence of equimolar mixtures of saturated and unsaturated acyl-CoAs were much different; the lung systems showed relatively higher selectivities for palmitate than the liver systems in the formation of both diacylglycerophosphate and phosphatidylcholine. On the other hand, palmitate was excluded almost completely from the 2-position in the 1-acylglycerophosphoethanolamine acyltransferase systems in lung and liver. These observations provide an enzymatic basis for describing the formation of pulmonary surfactant lipids in rat via acyltransferase systems.

Acyltransferase systems involved in phospholipid metabolism in Saccharomyces cerevisiae

Membrane preparations from Saccharomyces cerevisiae OC-2 catalyzed the acylation of glycerophosphate, 1-acyl and 2-acyl isomers of monoacylglycerophosphate, and 1-acyl and 2-acyl isomers of monoacylglycerylphosphorylcholine. The acyl-CoA:glycerophosphate acyltransferase system (EC 2.3.1.15) showed a broad specificity for acyl-CoAs when the maximal velocities were compared under optimized conditions. The acyl-CoA:2-acylglycerophosphate acyltransferase activity was much lower than the 1-acyl-glycerophosphate acyltransferase activity. Although the 1-acylglycerophosphate acyltransferase system utilized saturated and unsaturated acyl-CoAs at comparable rates, the acylations at the 1- and 2-positions were relatively more selective for palmitate and oleate, respectively, when assayed in the presence of palmitoyl-CoA, oleoyl-CoA, 1-acylglycerophosphate, and 2-acylglycerophosphate. The acyl-CoA:1-acylglyceryl-phosphorylcholine acyltransferase system (EC 2.3.1.23) was relatively more specific for unsaturated acyl-CoAs, while the acyl-CoA:2-acylglycerylphosphorylcholine acyltransferase system (EC 2.3.1.23) utilized both palmitoyl-CoA and oleoyl-CoA at a comparable rate. Although various acyltransferase systems showed a different degree of specificity for acyl-CoAs, the positional distribution of fatty acids in the phospholipid molecules could not be explained simply by the observed specificities. Zymolyase, β-1,3-glucanase from Arthrobacter luteus, was used successfully for the protoplast formation. Subcellular fractionation of the protoplast revealed that these acyltransferase activities were localized mainly in the microsomal fraction. However, the glycerophosphate and 1-acylglycerophosphate acyltranferase activities in the mitochondrial fraction could not be explained by the contamination of microsomes in this fraction. These observations are apparently inconsistent with a current concept that the mitochondrial fraction is the major site of phospholipid synthesis in yeast.

The glycerophosphateacyltransferases and their function in the metabolism of fatty acids.

1. From different studies on the cellular localization, postional specificity, and regulatory properties of acyl-CoA: glycerophosphate acyltransferase (EC 2,3,1.15) AND ACYL-CoA: 1-ACYLGLYCEROPHOSPHATE ACYLTRANSFERASE (EC 2,3,1....) the following conclusions can be drawn: The glycerophosphate acyltransferase is localized in the endoplasmatic reticulum (microsomes) and in the outer membrane of the mitochondria of the animal cell. Its reaction product is 1-acylglycerophosphate (1-lysophosphatidic acid). The mitochondrial enzyme shows a high preference for saturated fatty acids while the microsomal enzyme is less specific (alternatively the microsomes contain more than one glycerophsophate acyltransferase). 2. The 1-acylglycerphosphate acyltransferase is localized in the endoplasmatic reticulum (microsomes) in the animal cell. Possibly a minor fraction of this enzyme is localized to the outer membrane of the mitochondria. This enzyme shows a strong preference for unsaturated fatty acids. 3. Both the microsomal and the mitochondrial dihydroxyacetonephosphate acyltransferase show similar fatty acid specificity as the corresponding glycerophosphate acyltransferases. It cannot be excluded that dihydroxy-acetonephosphate and glycerophosphate are acylated by the same enzymes. 4. The activity of the glycerophosphate acyltransferase(s) in the liver decreases in fasting or fat feeding and increases upon feeding of carbohydrate. The activity of carnitine palmityltransferase varies exacty opposit. These enzymes do not show dietary variations in heart and adipose tissue. 5. Under the otherwise identical conditions the rate of carnitine acylation in isolated mitochondria decreases more than the rate of glycerophosphate acylation when the concentration of palmityl-CoA is reduced. 6. In isolated liver cells (which has lost most of their carnitine) addition of carnitine increases the rate of fatty acid oxidation and decreases the rate of triglyceride formation. 7. Glycerol and fructose lower the rate of fatty acid oxidation, probably by lowering the levels of acyl-CoA and acyl-carnitine in the cells. 8. It is concluded that the relative activities of glycerophosphate acyltranse and carnitine palmityltransferase probably influence the fate of fatty acids in the cell.

Factors affecting the acyl selectivities of acyltransferases in Escherichia coli.

In Escherichia coli the synthesis of phosphatidic acid from glycerophosphate involves first the intermediate formation of 1-acyl glycerophosphate. This reaction is catalyzed by the membrane-bound acyl-CoA(acyl-ACP):glycerophosphate acyltransferase. The 1-acylglycerophosphate is then converted to phosphatidic acid by acyl-CoA(acyl-ACP):1-acylglycerophosphate acyltransferase (Okuyama, H., and Wakil, S.J. (1973) J. Biol. Chem. 248, 5197-5205). In vitro both acyltransferases utilize various saturated and unsaturated acyl-CoAs at comparable rates, resulting in the incorporation of both saturated and unsaturated fatty acids into position 1 as well as position 2 of the glycerophosphate moiety. Thus, the specificities of acyltransferase systems as compared with regard to the maximal velocities for various acyl-AoAs, do not explain the positional distribution of the individual fatty acid in phospholipid molecules. The selectivities of the acyltransferases for acyl-CoAs are variable depending upon the acceptor concentration. In the presence of both palmitoyl-CoA and oleoyl-CoA and at low concentrations of the acceptors comparable to those found in vivo, the acylation at position 1 of glycerophosphate by acyl-CoA:glycerophosphate acyltransferase showed higher preference for palmitate, whereas the acylation at position 2 by acyl-CoA:1-acylglycerophosphate acyltransferase showed higher selectivity for oleate. In the presence of saturating amounts of the acceptors, the acylation at position 1 or position 2 was less selective for the acyl-CoAs. The ratios of saturated acyl-CoA to unsaturated acyl-CoA also affect the ratios of the fatty acids incorporated in vitro into positions 1 and 2 of phosphatidic acid; relatively more palmitate was incorporated when the proportion of palmitoyl-CoA among the acyl donors was higher and vice versa. Thus, highly selective positioning of various acyl-CoAs observed at lower concentrations of the acceptors in phosphatidic acid synthesis in vitro helps to explain the selective distribution of saturated and unsaturated fatty acids at positions 1 and 2 of glycerophospholipids in the membranes. Another factor, the availability of acyl donors, affects the proportions of different molecular species of phosphatidic acid, which at least partly explains the variability of molecular species of phospholipids found in vivo.

Acyl-donor specificities of partially purified 1-acylglycerophosphate acyltransferase, 2-acylglycerophosphate acyltransferase and 1-acylglycerophosphorylcholine acyltransferase from rat-liver microsomes.

1. A partially purified preparation containing 1‐acylglycerophosphate acyltransferase, 2‐acylglycerophosphate acyltransferase and 1‐acylglycerophosphorylcholine acyltransferase was obtained from rat liver microsomes which were resolved with a nonionic detergent, Triton X‐100, in glycine buffer pH 8.6. The purification procedure involves molecular sieve chromatography and sucrose density gradient centrifugation.2. The partially purified 1‐acylglycerophosphate acyltransferase exhibits a significant specificity for mono‐ and dienoic fatty acyl‐CoA thioesters. The effectiveness of the various acyl‐donors examined is as follows: oleyl‐CoA > linoleyl‐CoA ∼ palmitoleyl‐CoA > palmityl‐CoA ∼ myristyl‐CoA; arachidonyl‐CoA, stearyl‐CoA and lauryl‐CoA are almost ineffective. The newly formed ester bond is sensitive to the action of phospholipase A2.3. The partially purified 2‐acylglycerophosphate acyltransferase shows a predominant selectivity for saturated acyl‐CoA thioesters. Stearyl‐CoA is the most effective acyl‐donor, and palmityl‐CoA is utilized fairly efficiently.4. The partially purified 1‐acylglycerophosphorylcholine acyltransferase is specific for arachidonyl‐CoA.5. These findings, together with our previous studies on the acyl‐donor specificity of glycerophosphate acyltransferase, indicate that the asymmetric fatty acid distribution found in naturally occurring glycerolipids results mostly from the specific at the step of phosphatidic acid synthesis and partly from the deacylation‐reacylation cycle operating after the synthesis de novo of phospholipids.