51
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Jansen GJ, Pritzker CR, Deykin D. Porcine aortic endothelial cell membranes contain a LPAF: CoA-independent transacylase. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1145:113-8. [PMID: 8422403 DOI: 10.1016/0005-2736(93)90387-f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Membranes isolated from porcine aortic endothelial cells (PAEC) contain a CoA-independent transacylase enzyme (CoA-IT). CoA-IT, an integral membrane protein, transfers an acyl moiety to added [3H]alkylhydroxyglycerophosphocholine (LPAF) to generate [3H]alkylacylglycerophosphocholine (alkylacyl-GPC). This enzyme exhibits an apparent Km of 0.7 microM and a Vmax of 0.8 nmol/min per mg for the transfer of an acyl group to added [3H]LPAF. The addition of the nonionic detergent Triton X-100 (TX-100) (0.5 mg/ml), the sulfhydryl reagents N-ethylmaleimide (NEM) (200 microM) or thimerosal (200 microM), or pre-incubating the membranes at 95 degrees C for 10 min all decreased LPAF: CoA-IT activity by more than 95%. The inhibitory action of NEM or thimerosal suggests that sulfhydryl group(s) are involved in or are close to the catalytic site of LPAF: CoA-IT.
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Affiliation(s)
- G J Jansen
- Department of Medicine and Biochemistry, Boston University School of Medicine, MA
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52
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Winkler JD, Sung CM, Hubbard WC, Chilton FH. Evidence for different mechanisms involved in the formation of lyso platelet-activating factor and the calcium-dependent release of arachidonic acid from human neutrophils. Biochem Pharmacol 1992; 44:2055-66. [PMID: 1449523 DOI: 10.1016/0006-2952(92)90109-v] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Recent studies suggest that the first step in platelet-activating factor (PAF) biosynthesis, 1-alkyl-2-lyso-GPC (lyso PAF) formation, may be initiated by the selective transfer of arachidonate from 1-alkyl-2-arachidonoyl-GPC to an acceptor lyso phospholipid by a CoA-independent transacylase activity (CoA-IT). The present study was designed to determine whether the formation of 1-alkyl-2-lyso-GPC and the release of arachidonic acid can occur by different mechanisms. These experiments examined both the formation of 1-[3H]alkyl-2-lyso-GPC from 1-[3H]alkyl-2-acyl-GPC and the release of arachidonic acid from membrane phospholipids as determined by GC/MS in neutrophil homogenates under various conditions. The addition of unlabelled lyso phospholipids to neutrophil homogenates stimulated the time-dependent formation of 1-[3H]alkyl-2-lyso-GPC from 1-[3H]alkyl-2-acyl-GPC. Without exogenous lyso phospholipids, little 1-[3H]alkyl-2-lyso-GPC was formed in this reaction. The activity which catalyzed the formation of 1-[3H]alkyl-2-lyso-GPC had characteristics identical to CoA-IT as indicated by the fact that both reactions were: independent of Ca2+, Mg2+, CoA and CoA fatty acids, located in microsomal fractions, and stable in 10 mM dithiothreitol. In sharp contrast to the aforementioned reaction, addition of lyso phospholipids did not affect the quantity of arachidonic acid released from membrane phospholipids. Furthermore, there was a Ca(2+)-independent release of arachidonic acid from membrane phospholipid that was increased 4 to 5-fold after the addition of 5 mM Ca2+. Finally, Ca(2+)-dependent arachidonic acid release was inhibited by putative phospholipase A2 inhibitors, aristolochic acid and scalaradial, at concentrations where neither the production of 1-[3H]alkyl-2-lyso-GPC nor Ca(2+)-independent arachidonic acid release was altered. Together these data imply that there may be different mechanisms involved in the formation of 1-alkyl-2-lyso-GPC and arachidonic acid from membrane phospholipids.
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Affiliation(s)
- J D Winkler
- Division of Pharmacology, SmithKline Beecham Pharmaceuticals, King of Prussia, PA 19406
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53
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Lee T, Uemura Y, Snyder F. A novel CoA-independent transacetylase produces the ethanolamine plasmalogen and acyl analogs of platelet-activating factor (PAF) with PAF as the acetate donor in HL-60 cells. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)88655-6] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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54
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Frenkel R, Johnston J. Metabolic conversion of platelet-activating factor into ethanolamine plasmalogen in an amnion-derived cell line. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)41759-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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55
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Joly F, Breton M, Wolf C, Ninio E, Colard O. Heterogeneity of arachidonate and paf-acether precursor pools in mast cells. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1125:305-12. [PMID: 1596519 DOI: 10.1016/0005-2760(92)90060-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
In mammalian cells, arachidonate release and paf-acether formation are frequently associated. The alkyl-acyl-GPC has been proposed as an important source for released arachidonic acid and arachidonate-containing alkylacyl-GPC species as unique precursor for paf-acether. However, the specificity of precursor pools either concerning arachidonic acid or paf-acether is still a matter of controversy. We studied the relationship between the precursor pools for both autacoids in antigenically-stimulated cultured mast cells. We took advantage of the particular arachidonate turnover rate in each phospholipid to investigate the role of alkyl-arachidonyl-GPC in the supply of arachidonic acid by using newly and previously [14C]arachidonate-labeled cells. The specific activity of the released arachidonate was reduced 2-fold following overnight cell incubation, whereas labeling in alkyl-arachidonoyl-GPC was only slightly modified and never corresponded to that of released arachidonate when newly or previously labeled cells were triggered with the antigen. These results are not in favor of a major role for alkyl-arachidonoyl-GPC in supplying arachidonate. In contrast, by using previously labeled cells, we demonstrated that all arachidonate-containing phospholipids were involved in the release of arachidonic acid. The pattern of alkyl chains in alkyl-arachidonoyl-GPC, as well as in total alkylacyl-GPC, is unique since it consists mainly of 18:1 (more than 55%), whereas the 16:0 represents only about 30% of total alkyl chains. Therefore, we analyzed paf-acether molecular composition in order to compare it to the alkyl composition of the precursor pools. The content in 18:1 species of paf-acether, as measured by bioassay (aggregation of rabbit platelets), was always lower than that of 16:0 species and then did not correspond to the alkyl composition of the precursor. These data suggest that the enzymes involved in paf synthesis might be specific for 16:0 alkyl chains of precursor pool.
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Affiliation(s)
- F Joly
- INSERM U 200, Clamart, France
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56
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Affiliation(s)
- K Waku
- Faculty of Pharmaceutical Sciences, Teikyo University, Sagamiko, Kanagawa, Japan
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57
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58
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Snyder F, Lee TC, Blank ML. The role of transacylases in the metabolism of arachidonate and platelet activating factor. Prog Lipid Res 1992; 31:65-86. [PMID: 1641397 DOI: 10.1016/0163-7827(92)90016-c] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- F Snyder
- Oak Ridge Associated Universities, Medical Sciences Division, TN 37831-0117
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59
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Sugiura T, Ojima-Uchiyama A, Masuzawa Y, Fujita M, Nakagawa Y, Waku K. Regulation of the biosynthesis of platelet-activating factor in alveolar macrophages. Lipids 1991; 26:974-8. [PMID: 1819752 DOI: 10.1007/bf02536487] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Activities of enzymes which metabolize lysoplatelet-activating factor (lysoPAF) and platelet-activating factor (PAF) were studied in rabbit alveolar macrophage lysates. Substantial acetyltransferase activity was noted in the presence of 100 microM acetyl-coenzyme A (CoA), and this activity was increased in A23187-stimulated cell lysate. On the other hand, in the absence of exogenous acetyl-CoA, lysoPAF was mainly acylated through a transacylation pathway rather than by acetyltransferase in both control and A23187-stimulated cell lysates. We confirmed that the intracellular concentration of acetyl-CoA is relatively low. The observations suggest that the transacylation system may play an equally important role in the regulation of the availability of lysoPAF in intact cells. Intracellular lysoPAF was also maintained at relatively low levels. Interestingly, large amounts of PAF were produced even in unstimulated cells upon addition of an excess of exogenous lysoPAF, suggesting that generation of an adequate amount of lysoPAF within cells may be sufficient to trigger PAF synthesis in this type of cells.
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Affiliation(s)
- T Sugiura
- Faculty of Pharmaceutical Sciences, Teikyo University, Kanagawa, Japan
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60
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Chilton FH, Cluzel M, Triggiani M. Recent advances in our understanding of the biochemical interactions between platelet-activating factor and arachidonic acid. Lipids 1991; 26:1021-7. [PMID: 1819686 DOI: 10.1007/bf02536495] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In the last few years, it has become increasingly apparent that the biochemistry of PAF (platelet-activating factor) and that of arachidonic acid are interrelated in a number of inflammatory cells. Experiments presented here further point out that arachidonic acid plays a crucial role in the catabolism and biosynthesis of PAF. In addition, they suggest that the same phospholipid molecular species may serve as a source for both arachidonic acid and 1-alkyl-2-lyso-sn-glycero-3-phosphocholine during cell activation. Finally, they reveal that there may be common regulatory mechanisms for the biosynthesis of PAF and arachidonic acid metabolites. Taken together, studies examining the relationship between PAF and arachidonic acid suggest it may be difficult to consider the biochemistry of PAF without considering arachidonic acid metabolism and vice versa.
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Affiliation(s)
- F H Chilton
- Johns Hopkins University School of Medicine, Johns Hopkins Asthma and Allergy Center, Baltimore, Maryland 21224
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61
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Sugiura T, Ojima T, Fukuda T, Satouchi K, Saito K, Waku K. Production of platelet-activating factor in slugs. J Lipid Res 1991. [DOI: 10.1016/s0022-2275(20)41634-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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62
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Sugiura T, Fukuda T, Cheng NN, Waku K. Transient activation of 1-O-alkyl-sn-glycero-3-phosphocholine: acetyl-CoA acetyltransferase during the incubation of macrophages. Lipids 1991; 26:861-5. [PMID: 1805090 DOI: 10.1007/bf02535968] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The activity of the platelet-activating factor (PAF)-synthesizing enzyme, 1-O-alkyl-sn-glycero-3-phosphocholine (lysoPAF):acetyl-CoA acetyltransferase (EC 2.3.1.67) in alveolar macrophage lysate was found to be elevated after warming the cells to 37 degrees C. Such an increase in enzyme activity was detectable only when intact cells were warmed. The stimulation was transient, reaching a peak at 2 min, and then gradually decreased to the control level. We could not find increased PAF formation in warmed cells which had increased acetyltransferase activity, even though substantial amounts of lysoPAF were shown to be present within cells. In contrast, considerable amounts of PAF were formed after treatment of the cells with exogenous lysoPAF. These results suggest that the activation of acetyltransferase is not sufficient to induce PAF formation and that the increased availability of substrates, especially lysoPAF, in the cells is indispensable for triggering PAF biosynthesis in this type of cells.
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Affiliation(s)
- T Sugiura
- Faculty of Pharmaceutical Sciences, Teikyo University, Kanagawa, Japan
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63
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Sugatani J, Fujimura K, Mizuno T, Sameshima Y, Saito K. The role of platelet activating factor (PAF) in the pathogenesis of gastric ulcers. Prostaglandins Leukot Essent Fatty Acids 1991; 44:135-47. [PMID: 1808623 DOI: 10.1016/0952-3278(91)90048-a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- J Sugatani
- Department of Medical Chemistry, Kansai Medical University, Osaka, Japan
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64
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Venable M, Nieto M, Schmitt J, Wykle R. Conversion of 1-O-[3H]alkyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine to lyso platelet-activating factor by the CoA-independent transacylase in membrane fractions of human neutrophils. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)55118-8] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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65
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Chapkin RS, Coble KJ. Utilization of gammalinolenic acid by mouse peritoneal macrophages. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1085:365-70. [PMID: 1655039 DOI: 10.1016/0005-2760(91)90141-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
To delineate the metabolism of gammalinolenic acid (18:3(n-6] by macrophages, primary cultures of resident mouse peritoneal macrophages were incubated with [14C]18:3(n-6). At 3, 6 or 20 h, the majority (greater than 85%) of the radiolabel was recovered in cell phospholipids. With increasing time of incubation, a relative reduction of 14C in glycerophosphocholine (ChoGpl, 58.1% to 46.2%) was noted. This was offset by a corresponding increase in glycerophosphoethanolamine (EtnGpl) labeling (from 8.8% to 18.9%). There was also a time-dependent redistribution of 14C from diacyl to ether-containing phospholipid subclasses in ChoGpl and EtnGpl. Analysis of cell extracts by reverse-phae HPLC following transmethylation demonstrated that 18:3(n-6) was extensively elongated (greater than 80%) to dihomogammalinolenic acid (20:3(n-6] by 3 h. The major radiolabeled phospholipid molecular species in the diacyl (PtdCho) and alkylacylglycerophosphocholine (PakCho) subclasses was 16:0-20:3(n-6). In contrast, diacyl (PtdEtn) and alkenylacylglycerophosphoethanolamine (PlsEtn) subclasses contained primarily [14C]18:0-20:3(n-6) and 16:0-20:3(n-6), respectively. Macrophages prelabeled with [14C]18:3(n-6) for 20 h and stimulated with calcium ionophore A23187 or zymosan synthesized [14C]prostaglandin E1 (PGE1). These data demonstrate that macrophages possess an active long chain polyunsaturated fatty acid elongase capable of converting 18:3(n-6) to 20:3(n-6) which can, upon stimulation, be converted to PGE1.
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Affiliation(s)
- R S Chapkin
- Department of Animal Science, Texas A & M University, College Station 77843-2471
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66
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Nieto M, Venable M, Bauldry S, Greene D, Kennedy M, Bass D, Wykle R. Evidence that hydrolysis of ethanolamine plasmalogens triggers synthesis of platelet-activating factor via a transacylation reaction. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)55119-x] [Citation(s) in RCA: 97] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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67
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Reid T, Ramesha C, Ringold G. Resistance to killing by tumor necrosis factor in an adipocyte cell line caused by a defect in arachidonic acid biosynthesis. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)55340-0] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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68
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Winkler JD, Sung CM, Huang L. CoA-independent transacylase has characteristics distinct from those of PLA2 enzymes. AGENTS AND ACTIONS 1991; 34:103-5. [PMID: 1793010 DOI: 10.1007/bf01993250] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
CoA-independent transacylase (CoA-IT) catalyzes the transfer of arachidonic acid from acyl- to alkyl-linked phospholipids. The removal of arachidonic acid from the sn-2 position of the donor phospholipid is a PLA2-like reaction. However, examination of CoA-IT in U937 cells demonstrated that CoA-IT has many characteristics that are distinct from those of PLA2 enzymes, including activity in the absence of Ca2+, activity that was heat and acid unstable and stable in 10 mM 2-mercaptoethanol and that was inhibited by detergents. Compounds that inhibit PLA2 activity did not inhibit CoA-IT activity, including quinacrine, aristolochic acid and arachidonic acid. All of these characteristics of CoA-IT are in contrast to those of most PLA2 enzymes. These data suggest that CoA-IT is biochemically different from, and has a mechanism of action unique from PLA2 enzymes.
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Affiliation(s)
- J D Winkler
- Department of Pharmacology, SmithKline Beecham Pharmaceutials, King of Prussia, PA 19406
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69
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Lee TC, Blank ML, Fitzgerald V, Snyder F. Acylation of alkyllysophospholipids by Fischer sarcoma microsomes. Arch Biochem Biophys 1991; 288:600-8. [PMID: 1898052 DOI: 10.1016/0003-9861(91)90242-b] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Acylation of alkyllysophospholipids in most cells occurs by: (a) CoA-independent transacylation, (b) CoA-dependent transacylation, and (c) acyl-CoA-dependent acylation. Using a recently developed high-performance liquid chromatography method, we have investigated the factors that influence the molecular species composition of the acylated products formed via these pathways with 1-hexadecyl-2-lyso-sn-glycero-3-phosphocholine (alkyllyso-GPC) or 1-hexadecyl-2-lyso-sn-glycero-3-phospho-ethanolamine (alkyllyso-GPE) as substrates for the enzymes in Fischer R-3259 sarcoma microsomes. We found that short incubation times and low substrate concentrations favored the formation of polyunsaturated molecular species, i.e., 16:0-22:6, 16:0-22:5 (n - 3), and 16:0-20:4. Also, in agreement with results from other systems, CoA-independent transacylation produced a high percentage of polyunsaturated molecular species; acyl-CoA-dependent acylations generated the least polyunsaturated molecular species and CoA-dependent transacylation gave intermediate values. Furthermore, no substrate selectivity occurred with respect to alkyl chain lengths of alkyllyso-GPE; similar molecular species composition was obtained with either hexadecyllyso-GPE or octadecyllyso-GPE as substrates. Responses to N-ethylmaleimide inhibition and heat inactivation as well as pH optima suggest the same enzyme catalyzes the CoA-independent transacylation of both alkyllyso-GPC and alkyllyso-GPE.
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Affiliation(s)
- T C Lee
- Medical Sciences Division, Oak Ridge Associated Universities, Tennessee 37831-0117
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70
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MacDonald JI, Sprecher H. Phospholipid fatty acid remodeling in mammalian cells. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1084:105-21. [PMID: 1854795 DOI: 10.1016/0005-2760(91)90209-z] [Citation(s) in RCA: 247] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- J I MacDonald
- Department of Medical Biochemistry, Ohio State University, Columbus 43210
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71
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Abstract
PAF is known to be produced by two independent enzymatic pathways. The remodeling route involves structural modification of a membrane phospholipid (1-alkyl-2-acyl-sn-glycero-3-phosphocholine) by substitution of an acetate for the acyl group at the sn-2 position. In contrast, the de novo pathway includes a sequence of acetylation, dephosphorylation, and phosphocholine addition, starting with the alkyl analog of lyso-phosphatidic acid. Hypersensitivity reactions with PAF as the autacoid are triggered by activation of the remodeling enzymes to produce excessive amounts of PAF. Inactivation of PAF occurs primarily by hydrolysis of the acetate group in a reaction catalyzed by acetylhydrolase. Results of our studies indicate that biosynthesis and catabolism of PAF by membrane preparations from both lung tissue and alveolar macrophages are qualitatively similar to that found in other cells. All of the enzymatic activities for both the remodeling and de novo pathways of PAF biosynthesis occur in the lung. Recent experiments indicate the initial reaction that produces lyso-PAF in the remodeling pathway of PAF biosynthesis is under the control of a CoA-independent transacylase that is capable of catalyzing both the hydrolysis of the acyl moiety of the alkylacylglycerophosphocholine precursor and its transfer to another lyso-phospholipid. The substrate specificity for the phospholipase A2 component of this reaction is for alkylacylglycerophosphocholines possessing arachidonate at the sn-2 position. Other polyunsaturated alkylacylglycerophosphocholines appear to be utilized as PAF precursors too, albeit to a lesser extent than the 20:4 species. The CoA-independent transacylase and its high affinity for the transfer of arachidonate to lyso-PAF appears to be a very prominent enzyme activity in rat lung membranes.
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Affiliation(s)
- F Snyder
- Medical Sciences Division, Oak Ridge Associated Universities, Tennessee 37831-0117
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72
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Pool GL, Samples B, Turner MR, Lumb RH. Acylation of lyso platelet-activating factor by splenocytes of the rainbow trout, Oncorhyncus mykiss. Lipids 1991; 26:517-20. [PMID: 1943495 DOI: 10.1007/bf02536596] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
In mammalian systems, platelet-activating factor, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, (PAF) is rapidly inactivated by a deacetylation/reacylation system that produces 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine which is highly enriched in arachidonic acid. There is some evidence that n-3 fatty acids may have an impact on this system in humans but the nature of this impact is unclear. In rainbow trout, n-3 fatty acids are known to be essential dietary components which are derived through the food chain. Substantial quantities of n-3 fatty acids are found in trout membrane phospholipids. We show here that in sharp contrast to mammalian cells, trout cells acylate lyso platelet-activating factor, alkyl-GPC, 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine, (lyso-PAF) with a high degree of specificity for n-3 fatty acids. When [3H]lysoPAF was incubated with these cells, only three molecular species of alkylacylglycerophosphocholine were produced, and 92% contained n-3 fatty acids. Since isolated membranes yielded similar results, it appears that the acylation proceeds via a coenzyme A-independent transacylase as found in mammalian systems.
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Affiliation(s)
- G L Pool
- Mountain Aquaculture Research Center, Western Carolina University, Cullowhee, North Carolina 28723
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73
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A coenzyme A-independent transacylase is linked to the formation of platelet-activating factor (PAF) by generating the lyso-PAF intermediate in the remodeling pathway. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)92972-8] [Citation(s) in RCA: 111] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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74
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Winkler JD, Sung CM, Bennett CF, Chilton FH. Characterization of CoA-independent transacylase activity in U937 cells. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1081:339-46. [PMID: 1900206 DOI: 10.1016/0005-2760(91)90291-o] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Coenzyme A-independent transacylase (CoA-IT) mediates the transfer of polyunsaturated fatty acids from the sn-2 position of a donor phospholipid to the sn-2 position of an acceptor lyso-phospholipid. We have characterized this activity in U937 cells, a human monocytic cell line. The microsomes of these cells contained CoA-IT activity which demonstrated a fatty acid preference for transferring arachidonic acid into exogenously added 1-alkyl-2-lyso-GPC. This enzymatic activity was optimum between pH 6.5 and 9, was heat labile and displayed an apparent Km for 1-alkyl-2-lyso-GPC of 0.4 microM. This activity was not dependent on Ca2+, Mg2+, CoA or ATP, was not inhibited by 2-mercaptoethanol nor by addition of product, 1-alkyl-2-acyl-GPC. The activity of this enzyme was not altered by differentiation of U937 cells towards the macrophage with Me2SO. Treatment of U937 cells with dexamethasone had no effect on transacylase activity. The activity of this enzyme was decreased by the serine esterase inhibitors phenylmethyl-sulfonyl fluoride and N-tosyl-L-phenylalanine chloromethyl ketone and by the histidine modifier diethyl pyrocarbonate, suggesting that CoA-IT may belong to a family of acyltransferase enzymes typified by LCAT. CoA-IT activity was not affected by compounds that affect PLA2 activity, such as quinacrine, aristolochic acid and arachidonic acid, suggesting a mechanism of action for CoA-IT different from classical, low molecular weight PLA2 enzymes. In conclusion, U937 cells contain CoA-IT activity and this study extends our previous knowledge of this enzyme by demonstrating the differences between CoA-IT and PLA2 enzymes and suggesting similarities between CoA-IT and LCAT.
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Affiliation(s)
- J D Winkler
- Department of Pharmacology, SmithKline Beecham Pharmaceuticals, King of Prussia, PA 19406
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75
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Sugiura T, Fukuda T, Masuzawa Y, Waku K. Ether lysophospholipid-induced production of platelet-activating factor in human polymorphonuclear leukocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1047:223-32. [PMID: 2123719 DOI: 10.1016/0005-2760(90)90520-8] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Human polymorphonuclear leukocytes (PMN) produced considerable amounts of platelet-activating factor (PAF) when exposed to various concentrations of lyso-PAF, especially in the absence of albumin. The amount of produced PAF in the presence of 5 microM lyso-PAF (without albumin) was 1.1 pmol/10 min per 2.5 X 10(6) cells, which was close to the level in the case of opsonized zymosan stimulation. We found that the activity of neither acetyltransferase nor acetylhydrolase was affected markedly by the treatment of cells with lyso-PAF, suggesting that the increased availability of lyso-PAF could be responsible for the induction of PAF synthesis. We also found that PAF synthesis was induced not only by lyso-PAF but also by ether-containing ethanolamine lysophospholipids, 1-alkenyl(alkyl)-sn-glycero-3-phosphoethanolamine (GPE). The addition of 1-alkenyl(alkyl)-GPE caused the degradation of pre-existing 1-alkyl-2-arachidonoyl-sn-glycero-3-phosphocholine (GPC) and an increased level of lyso-PAF, followed by the formation of PAF. By contrast, 1-acyl-GPC and 1-acyl-GPE failed to induce PAF production. These results suggest a possible key role of the availability of lyso-PAF in triggering the biosynthesis of PAF in human PMN.
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Affiliation(s)
- T Sugiura
- Faculty of Pharmaceutical Sciences, Teikyo University, Kanagawa, Japan
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76
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Tessner TG, Greene DG, Wykle RL. Selective deacylation of arachidonate-containing ethanolamine-linked phosphoglycerides in stimulated human neutrophils. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(17)45323-3] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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77
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Snyder F. Platelet-activating factor and related acetylated lipids as potent biologically active cellular mediators. THE AMERICAN JOURNAL OF PHYSIOLOGY 1990; 259:C697-708. [PMID: 2240190 DOI: 10.1152/ajpcell.1990.259.5.c697] [Citation(s) in RCA: 284] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Platelet-activating factor (PAF or 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is the most potent lipid mediator yet discovered. It is known to stimulate a wide span of biological responses ranging from aggregation and degranulation of platelets and neutrophils to a variety of cellular effects involving the stimulation of chemotaxis; chemokinesis; superoxide formation; protein phosphorylation; activation of protein kinase C, arachidonic acid, and phosphoinositide metabolites; glycogenolysis; and tumor necrosis factor production. Obviously, with such a diversity of biological activities, it is not surprising that PAF has been considered to be a key component in numerous diseases related to hypersensitivity and inflammatory responses. Evidence has also been presented for the role of PAF in physiological processes, particularly those involving reproduction and fetal development. Furthermore, because of its potent hypotensive action, PAF has been implicated as a contributing factor in blood pressure regulation. PAF is produced by two independent enzymatic pathways. The remodeling route involves the structural modification of a membrane lipid (1-alkyl-2-acyl-sn-glycero-3-phosphocholine) by replacement of the acyl moiety with an acetate group. An alternate route is the de novo synthesis of PAF from an O-alkyl analogue of a lysophosphatidic acid that requires a reaction sequence of acetylation, dephosphorylation, and phosphocholine addition steps. Hypersensitivity and other pathophysiological reactions are thought to be caused by activation of the remodeling pathway, whereas the de novo route is believed to be the source of endogenous levels of PAF required for physiological functions. Inactivation of PAF occurs when the acetate group is hydrolyzed by an acetylhydrolase that is present in both extra- and intracellular compartments, although the catalytic activity of the two forms of acetylhydrolase are identical, some of their properties differ. The control of PAF metabolism is very complex, but acetylhydrolase, Ca2+, phosphorylation/dephosphorylation of enzymes, and fatty acids (especially polyunsaturates) appear to be important regulatory factors. Specific PAF receptors have clearly been demonstrated on several different types of cells, and although the mechanism of PAF actions is poorly understood, it appears that the PAF/receptor-induced responses are closely associated with the signal transduction process; both G proteins and adenyl cyclase appear to be involved. Because significant quantities of PAF are often retained within certain cells, the possibility of PAF serving as an intracellular mediator has also been proposed.
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Affiliation(s)
- F Snyder
- Medical Sciences Division, Oak Ridge Associated Universities, Tennessee 37831-0117
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78
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Masrar H, Bereziat G, Colard O. Very high proportion of disaturated molecular species in rat platelet diacyl-glycerophosphocholine: involvement of CoA-dependent transacylation reactions. Arch Biochem Biophys 1990; 281:116-23. [PMID: 2116766 DOI: 10.1016/0003-9861(90)90420-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The molecular species composition of rat platelet diacyl-glycerophosphocholine (GPC) was investigated by reverse-phase HPLC and by mass spectrometry. The two methods gave the same very high proportion of fully saturated phospholipids, the 16:0-16:0 and 16:0-18:0 species representing together about 40% of the overall molecular species. [14C]Palmitoyllyso-GPC was found to be acylated by resting platelets in equal amounts into 16:0-16:0 and into 16:0-20:4 species. The acylation rate of this lysophospholipid was increased by 3-fold and 14-fold when platelets were stimulated for 10 min with thrombin and the ionophore A23187, respectively. Essentially the same two molecular species were synthesized upon stimulation but with a higher preference for arachidonate than for palmitate. We investigated the mechanisms responsible for the incorporation of palmitate and arachidonate by examining the enzymatic acylation of [14C]palmitoyllyso-GPC by platelet homogenates. The percentage of the various molecular species formed when CoA, ATP, and Mg2+ were added excludes the CoA, ATP-dependent pathway as being involved in the acylation reactions previously observed. In the absence of ATP, CoA-independent transacylations appear to play a crucial role in the synthesis of the 16:0-20:4 species whereas the addition of CoA greatly favored dipalmitoyl-GPC synthesis. The involvement of CoA-dependent mechanisms in the synthesis of dipalmitoyl-GPC was demonstrated as follows: (i) the labeling in the sn-2 position of the dipalmitoyl-GPC synthesized in the presence of CoA was not modified when free unlabeled palmitic acid was added to the incubation medium and (ii) platelet homogenates were unable to esterify lysolecithin with added labeled palmitic acid in the presence of CoA only.
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Affiliation(s)
- H Masrar
- CNRS, URA 1283, Biochimie, C.H.U. Saint-Antoine, Paris, France
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79
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80
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Snyder F, Lee TC, Blank ML. Platelet-activating factor and related ether lipid mediators. Biological activities, metabolism, and regulation. Ann N Y Acad Sci 1989; 568:35-43. [PMID: 2698076 DOI: 10.1111/j.1749-6632.1989.tb12488.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- F Snyder
- Medical Sciences Division, Oak Ridge Associated Universities, Tennessee 37831-0117
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81
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Triggiani M, Chilton FH. Influence of immunologic activation and cellular fatty acid levels on the catabolism of platelet-activating factor within the murine mast cell (PT-18). BIOCHIMICA ET BIOPHYSICA ACTA 1989; 1006:41-51. [PMID: 2572273 DOI: 10.1016/0005-2760(89)90321-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The present study has examined the catabolism of 1-O-[3H]hexadecyl-2-acetyl-GPC (C16-PAF) and of 1-O-octadecyl-2-acetyl-GPC (C18-PAF) in spleen-derived PT-18 murine mast cells (mast cells). Mast cells catabolized exogenous PAF into two inactive metabolites, 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine (lysoPAF) and 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine (1-O-alkyl-2-acyl-GPC). The rate of conversion of C16-PAF to metabolites was more rapid than that of C18-PAF. Analysis of the acyl composition of 1-O-alkyl-2-acyl-GPC formed during the metabolism of PAF revealed that arachidonic acid (20:4) was the major fatty acyl chain incorporated at the sn-2 position. However, 25% of newly formed 1-O-alkyl-2-acyl-GPC was reacylated with docosahexaenoic acid (22:6). The influence of cellular fatty acid content on PAF catabolism was further explored in mast cells in which the ratio of fatty acids within cellular phosphoglycerides had been altered by supplementing the cells with various fatty acids in culture. Mast cells supplemented with 20:4 or 22:6 converted PAF to 1-O-alkyl-2-acyl-GPC at a significantly higher rate than non-supplemented cells. In contrast, cells supplemented with linoleic acid (18:2) metabolized PAF at rates similar to non-supplemented cells. Analysis of the acyl composition of 1-O-alkyl-2-acyl-GPC derived from the metabolism of PAF in 20:4-supplemented cells indicated that 20:4 was incorporated exclusively into the sn-2 position. Conversely, 22:6-supplemented cells incorporated predominantly 22:6 at the sn-2 position of 1-alkyl-2-lyso-GPC. Supplementation with 18:2 had no effect on the acylation pattern seen in newly formed 1-O-alkyl-2-acyl-GPC. Activation of passively sensitized mast cells with antigen or with ionophore A23187 significantly enhanced the rate of catabolism of exogenously-provided PAF but had no effect on the acylation pattern of 1-O-alkyl-2-acyl-GPC. Experiments performed with the soluble fraction of the cells showed that acetyl hydrolase activity was increased in mast cells stimulated with antigen. In addition, supernatant fluids from antigen or ionophore-treated mast cells converted PAF to lysoPAF, suggesting that acetyl hydrolase activity was released during cell activation. These data indicate that the ability of mast cells to catabolize PAF to inactive metabolites is influenced by cell activation and by the cellular levels of certain fatty acids.
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Affiliation(s)
- M Triggiani
- Department of Medicine, Johns Hopkins University School of Medicine, Good Samaritan Hospital, Baltimore, MD 21239
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82
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Distribution of arachidonic acid in choline- and ethanolamine-containing phosphoglycerides in subfractionated human neutrophils. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(19)84630-6] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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83
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Masuzawa Y, Sugiura T, Sprecher H, Waku K. Selective acyl transfer in the reacylation of brain glycerophospholipids. Comparison of three acylation systems for 1-alk-1'-enylglycero-3-phosphoethanolamine, 1-acylglycero-3-phosphoethanolamine and 1-acylglycero-3-phosphocholine in rat brain microsomes. BIOCHIMICA ET BIOPHYSICA ACTA 1989; 1005:1-12. [PMID: 2673414 DOI: 10.1016/0005-2760(89)90024-6] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The activities of three acylation systems for 1-alkenylglycerophosphoethanolamine (1-alkenyl-GPE), 1-acyl-GPE and 1-acylglycerophosphocholine (1-acyl-GPC) were compared in rat brain microsomes and the acyl selectivity of each system was clarified. The rate of CoA-independent transacylation of 1-[3H]alkenyl-GPE (approx. 4.5 nmol/10 min per mg protein) was about twice as high as in the case of 1-[3H]acyl-GPE and 1-[14C]acyl-GPC. On the other hand, the rates of CoA-dependent transacylation and CoA + ATP-dependent acylation (acylation of free fatty acids by acyl-CoA synthetase and acyl-CoA acyltransferase) of lysophospholipids were in the order 1-acyl-GPC greater than 1-acyl-GPE much greater than 1-alkenyl-GPE. HPLC analysis of newly synthesized molecular species revealed that the CoA-independent transacylation system exclusively esterified docosahexaenoate and arachidonate, regardless of the lysophospholipid class. The CoA-dependent transacylation and CoA + ATP-dependent acylation systems were almost the same with respect to the selectivities for unsaturated fatty acids when the same acceptor lysophospholipid was used, but some distinctive acyl selectivities were observed with different acceptor lysophospholipids. 1-Alkenyl-GPE selectively acquired only oleate in these two systems. 1-Acyl-GPE and 1-acyl-GPC showed selectivities for both arachidonate and oleate. In addition, an appreciable amount of palmitate was transferred to 1-acyl-GPC, not to 1-acyl-GPE, in CoA- or CoA + ATP-dependent manner. The acylation of exogenously added acyl-CoA revealed that the acyl selectivities of the CoA-dependent transacylation and CoA + ATP-dependent acylation systems may be mainly governed through the selective action of acyl-CoA acyltransferase. The preferential utilization of oleoyl-CoA by all acceptors and the different utilization of arachidonoyl-CoA between alkenyl and acyllysophospholipids indicated that there might be two distinct acyl-CoA:lysophospholipid acyltransferases that discriminate between oleoyl-CoA and arachidonoyl-CoA, respectively. Our present results clearly show that all three microsomal acylation systems can be active in the reacylation of three major brain glycerophospholipids and that the higher contribution of the CoA-independent system in the reacylation of ethanolamine glycerophospholipids, especially alkenylacyl-GPE, may tend to enrich docosahexaenoate in these phospholipids, as compared with in the case of diacyl-GPC.
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Affiliation(s)
- Y Masuzawa
- Faculty of Pharmaceutical Sciences, Teikyo University, Kanagawa, Japan
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84
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MacDonald JI, Sprecher H. Studies on the incorporation and transacylation of various fatty acids in choline and ethanolamine-containing phosphoacylglycerol subclasses in human neutrophils. BIOCHIMICA ET BIOPHYSICA ACTA 1989; 1004:151-7. [PMID: 2752015 DOI: 10.1016/0005-2760(89)90263-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The incorporation of eight 14C-labeled fatty acids into human neutrophil phospholipids was investigated and the results were expressed as percent of the total phospholipid associated 14C-labeled substrate incorporated after an initial 15 min labeling and a subsequent 2 h reincubation in fatty acid-free buffer. In all cases, the PC fraction accounted for more than 40% of the total phospholipid radioactivity. The inositol-containing phosphoacylglycerols were also labeled well by all the fatty acids except 22:6(n - 3) and 16:0; however, a greater percentage of [14C]22:6(n - 3) was found in PE than that of any other labeled fatty acid substrate. In all cases, most of the radioactivity in PC after 15 min was in the diacyl subclass. After 2 h, there was a shift of [14C]20:4(n - 6), [14C]20:5(n - 3), [14C]22:6(n - 3) and [14C]18:4(n - 4) into the ether-linked subclass. No such shift was observed for [14C]16:0 or [14C]18:2(n - 6) and, although there was an increase in the percent radioactive 20:3(n - 6) and 20:3(n - 9) in ether-linked PC after 2 h, the total radioactivity in this fraction remained low by comparison. A similar shift in label occurred in the plasmalogenic-linked PE subspecies in cells labeled with [14C]20:4(n - 6), [14C]20:5(n - 3) and [14C]22:6(n - 3).
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Affiliation(s)
- J I MacDonald
- Department of Physiological Chemistry, Ohio State University, Columbus 43210
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85
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Kadiri C, Masliah J, Bachelet M, Vargaftig BB, Béréziat G. Phospholipase A2-mediated release of arachidonic acid in stimulated guinea pig alveolar macrophages: interaction with lipid mediators and cyclic AMP. J Cell Biochem 1989; 40:157-64. [PMID: 2549080 DOI: 10.1002/jcb.240400204] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The stimulation of cultured guinea pig alveolar macrophages by the chemotactic peptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine, or by the phospholipid inflammatory mediator platelet activating factor (PAF) induced an increase in arachidonic acid release and its cyclooxygenase products. This release, which was mimicked by the association of threshold concentrations of the calcium ionophore A 23187 and of the protein kinase C activator tetradecanoyl phorbol acetate arose mainly from diacyl- and alkyl-acyl-phosphatidylcholine and phosphatidylinositol. Using [1-14C]arachidonic acid-labeled membranes as an endogenous substrate as well as dioleoyl-phosphatidyl [14C]ethanolamine as an exogenous substrate, we showed that phospholipase A2 activity of stimulated macrophages increases upon stimulation. Treatment of macrophages by prostaglandin E2 decreased the arachidonic acid release elicited by the chemotactic peptide and PAF. Furthermore, prostaglandin E2 increased and PAF decreased the cellular content in cyclic AMP. From these results we suggest that an initial stimulation of alveolar macrophages by a bacterial signal initiates the sequential activation of a phospholipase C and of phospholipase A2, leading to the release of PAF and eicosanoids. These mediators may in turn modulate the cell response by increasing or decreasing cyclic AMP, Ca2+, or diacyglycerol macrophage content.
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Affiliation(s)
- C Kadiri
- Department of Biochemistry, CNRS URA 1283, Faculté de Médecine Saint Antoine, Paris, France
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86
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Nakagawa Y, Waku K. The metabolism of glycerophospholipid and its regulation in monocytes and macrophages. Prog Lipid Res 1989; 28:205-43. [PMID: 2694177 DOI: 10.1016/0163-7827(89)90013-1] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Y Nakagawa
- Faculty of Pharmaceutical Sciences, Teikyo University, Kanagawa, Japan
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87
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Zimmerman WF, Keys S. Lysophospholipase and the metabolism of lysophosphatidylcholine in isolated bovine rod outer segments. Exp Eye Res 1989; 48:69-76. [PMID: 2920784 DOI: 10.1016/0014-4835(89)90020-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Incubation of bovine rod outer segments (ROS) with radiolabeled palmitic acid (16:0) and lysophosphatidylcholines (lysoPC) radiolabeled in either the fatty acid or the choline group indicated the presence of a lysophospholipase activity that is unaffected by Ca2+. In the presence of ATP, Mg2+ and CoA and acyl CoA:lysophospholipid acytransferase activity is evident, and free fatty acids, including those released by lysophospholipase activity, are esterified to membrane phospholipids. At low concentrations of lysoPC, 68% of it is acylated to form phosphatidylcholine (PC) and 24% is converted to glycerophosphocholine (GPC) and fatty acid per hour. As the concentration of lysoPC increases lysophospholipase activity increases, acyl-CoA:lysophospholipid acyltransferase activity decreases, and the proportion of lysoPC converted to PC decreases. The rate of production of lysophospholipids in vitro under phospholipase A-stimulatory conditions exceeds the rate at which it can be removed by 5-10-fold. This suggests the possibility that an early step in light, anoxia- or hypoxia-induced damage to photoreceptor cells may be activation of the phospholipase A endogenous to ROS.
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88
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Careaga-Houck M, Sprecher H. Effect of a fish oil diet on the composition of rat neutrophil lipids and the molecular species of choline and ethanolamine glycerophospholipids. J Lipid Res 1989. [DOI: 10.1016/s0022-2275(20)38400-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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89
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90
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Banks JB, Wykle RL, O'Flaherty JT, Lumb RH. Evidence for protein-catalyzed transfer of platelet activating factor by macrophage cytosol. BIOCHIMICA ET BIOPHYSICA ACTA 1988; 961:48-52. [PMID: 3382692 DOI: 10.1016/0005-2760(88)90129-4] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Platelet activating factor (PAF) is a potent, proinflammatory lipid. PAF is synthesized in response to stimuli and is rapidly destroyed by specific acetylhydrolases. In order to express its biological activity, PAF and its metabolites are transported among subcellular membranes by as yet unexplained mechanisms. We report here an assay system using methylcarbamyl-PAF (CPAF, 1-O-hexadecyl-2-O-(N-methylcarbamyl)-sn-glycero-3-phosphocholine) and a vesicle-extrusion technique for examining protein-catalyzed intermembrane transfer of CPAF, and demonstrate the presence of proteins catalyzing the separate transfer of CPAF and diacyl phosphatidylcholine in macrophage cytosol. The CPAF transfer activity is heat- and trypsin-sensitive and elutes from gel-filtration columns well separated from proteins catalyzing the transfer of phosphatidylcholine.
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Affiliation(s)
- J B Banks
- Biochemistry Group, Western Carolina University, Cullowhee, NC 28723
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91
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Reddy PV, Schmid HH. Acylation of dog heart lysophosphatidylserine by transacylase activity. BIOCHIMICA ET BIOPHYSICA ACTA 1987; 922:379-85. [PMID: 3689816 DOI: 10.1016/0005-2760(87)90062-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Dog heart microsomes catalyze the transfer of acyl groups from the sn-2 position of phosphatidylcholine (PC) to lysophosphatidylserine (lysoPS) in the presence of coenzyme A (CoA) at pH optima of 4.5-5.0 and 7.5. Acyl transfer activity at acidic pH is about three times higher than at neutral pH. Transacylation of lysoPS by acyl transfer from PC with dog heart microsomes at neutral pH favors arachidonate over linoleate by a factor of 2.1, whereas free linoleic acid is favored by a factor of 3.7 over arachidonic acid for lysoPS acylation in the presence of acyl-CoA-generating cofactors. Considering the location and acyl composition of myocardial PS, it appears that both acyl transfer from PC and utilization of unesterified fatty acids may be involved in the acylation of lysoPS at its sn-2 position.
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Affiliation(s)
- P V Reddy
- Hormel Institute, University of Minnesota, Austin 55912
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92
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Neumüller W, Fleer EA, Unger C, Eibl H. Enzymatic acylation of ether and ester lysophospholipids in rat liver microsomes. Lipids 1987; 22:808-12. [PMID: 3444370 DOI: 10.1007/bf02535535] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The acylation of lysophospholipids by rat liver acyltransferases was studied. A comparison between ester and ether lysophospholipids as substrates revealed large differences in substrate properties. For instance, oleic acid from oleoyl-CoA and arachidonic acid from arachidonoyl-CoA were not incorporated into 1-O-octadecyl-sn-glycero-3-phosphocholine under experimental conditions that allowed an optimal transfer of oleic acid and arachidonic acid to 1-O-palmitoyl-sn-glycero-3-phosphocholine. However, we observed an acyl-CoA-independent transfer of arachidonic acid from 1-O-stearoyl-2-O-arachidonoyl-sn-glycero-3-phosphoinositol to 1-O-octadecyl-sn-glycero-3-phosphocholine.
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Affiliation(s)
- W Neumüller
- Max-Planck-Institut für biophysikalische Chemie, Göttingen, Federal Republic of Germany
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93
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Sugiura T, Sekiguchi N, Nakagawa Y, Waku K. Formation of diacyl and alkylacyl glycerophosphocholine in rabbit alveolar macrophages. Lipids 1987; 22:589-95. [PMID: 3657397 DOI: 10.1007/bf02537286] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The incorporation of various labeled precursors into alkenylacyl, alkylacyl and diacyl phospholipids in rabbit alveolar macrophages was studied. The incorporation rates of the individual precursors were shown to be quite different among the three subclasses of phospholipids. [3H]Glycerol, [14C]16:0, [14C]18:1, [14C]18:2 and [32P]-orthophosphate were preferentially incorporated into choline glycerophospholipids (CGP), especially into diacyl glycerophosphocholine (GPC), indicating that the de novo synthesis of diacyl GPC is extremely high. Considerable portions of the radioactivities of [14C]16:0, [14C]18:1, [14C]18:2 and [32P]orthophosphate were also found in alkylacyl GPC, the incorporation being higher than or comparable to that in the case of diacyl glycerophosphoethanolamine (GPE). We then examined the activities of cholinephosphotransferase and ethanol-aminephosphotransferase, and found that the activity of cholinephosphotransferase was remarkably high in macrophage microsomes compared with that in microsomes from several other tissues. This suggests that diradylglycerols were preferentially utilized by choline-phosphotransferase, which is consistent with the results obtained for intact cells. We confirmed that a considerably higher amount of diacyl GPC as well as alkylacyl GPC was formed through this enzyme reaction with macrophage microsomes than with brain microsomes. The high formation of alkylacyl GPC could be responsible, at least in part, for the accumulation of this unique ether phospholipid, a stored precursor form of platelet-activating factor in macrophages.
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Affiliation(s)
- T Sugiura
- Faculty of Pharmaceutical Sciences, Teikyo University, Kanagawa, Japan
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