Enzymic synthesis of ether types of choline and ethanolamine phosphoglycerides by microsomal fractions from rat brain and liver (original) (raw)
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Lipids, 1975
The transfer of radioactivity from cytidine-5'-diphosphate ethanolamine into 1-alk y 1-2-acyl-sn-glycerophosphorylethanolamine of neuronal and glial cells from adult rabbit brain cortex has been investigated in vitro. The synthesis of 1-alkyl-2a c yl-s n-gly cerophosphorylethanolamine in both cell populations was stimulated 23-25-fold by the addition of 6 mM alkylacylglycerol. The neuronal cell-enriched fraction was found to possess]unit protein a 1.7-1.8-fold ethanolaminephosphotransferase activity (EC 2.7.8.1), as compared to the glial fraction, when saturating concentrations (6 mM) of alkylacylglycerols were added in the incubation system. The neuronal/glial ratio was 2.6-2.8 in the absence of lipid acceptor or with low concentrations of alkylacylglycerol. Under most favorable conditions, 6.4 and 3.3 nmoles 1-alkyl-2a c y l-sn-gly cerophosphorylethanolamine/rag protein/30 min was obtained for neurons and glia, respectively. Various kinetic properties of the 1-alkyl-2-acylsn-glycerophosphorylethanolamine synthesizing phosphotransferase activity were found to be similar both in neurons and glia.
Journal of Lipid Research, 1976
Activities of ethanolaminephosphotransferases (EC 2.7.8.1) and choline phosphotransferases (EC 2.7.8.2) in microsomal fractions from brains and livers of mature rats are increased several fold by the addition of 1,2diacyl-sn-glycerols or 1-alkyl-2-acyl-sn-glycerols. Oleic acid added with diacylglycerols stimulated further the synthesis of lecithins by liver microsomes, confirming the work of Sribney and Lyman (Can. J. Biochem. 51: 1479-1486, 1973). With alkylacylglycerols, oleic and stearic acids were inhibitory and linoleic acid was even more inhibitory for the synthesis of both l-alkyl-2-acyl-sn-glycero-3-phosphorylcholines and the corresponding ethanolamine compounds with microsomes from both tissues. Free fatty acids without added diglycerides had mixed effects. These results are best explained by postulating the presence of two isoenzymes each for ethanolaminephosphotransferase and cholinephosphotransferase of which only one is affected by free fatty acids. Regulation of the phosphotransferases by free fatty acids may determine the proportion of CDP-choline and CDP-ethanolamine used for synthesis of diacyl and alkylacyl types of these phosphoglycerides.
FEBS Letters, 1987
The activity of CDP-choline-dependent glycerophosphorylcholine synthetase (CDP-choline:sn-3-glycerophosphate cholinetransferase), a newly discovered enzyme involved in the recently proposed pathways of acyl-specific phosphatidylcholine synthesis, is reported in rat liver. Endogenous CDP-choline, synthesized via the CMP-driven back reaction of phosphorylcholine transferase, is also shown to be a choline donor for this glycerophosphorylcholine synthetase. The function of glycerophosphorylcholine as an intermediate in phosphatidylcholine synthesis is demonstrated by specific isotope trapping whereby unlabelled glycerophosphorylcholine inhibited label incorporation from sn-[Wlglycerol-3-phosphate into phosphatidylcholine in mouse gastrocnemius, a tissue that is essentially devoid of the cytidine pathway for phosphatidylcholine synthesis and uses a non-allelic glycerophosphorylcholine synthetase (exogenous PC:sn-3-glycerophosphate cholinetransferase) in the synthesis of glycerophosphorylcholine.
Biosynthesis of rat brain phosphatidylethanolamines from intracerebrally injected ethanolamine
Brain Research, 1977
2-aH]Ethanolamine was injected intracerebrally into male rats and the brains of the animals immediately removed by particular procedures at regular intervals over the first 1200 sec. The incorporation of radioactivity into brain phosphorylethanolamine, cytidine-5'-diphosphate (CDP) ethanolamine and phosphatidylethanolamines was examined and quantitated. The nature of phosphatidylethanolamine molecular subspecies, which became labelled, was also investigated after isotope administration. Phosphorylethanolamine, CDP-ethanolamine and phosphatidylethanolamines were all labelled already 5 sec after the administration of labelled ethanolamine. The specific radioactivities of different phosphatidylethanolamine molecular subspecies varied according to the time elapsed from the injection to the sacrifice of the animals. This last result, together with the data on time course of labelling of ethanolamine phosphoglycerides and their precursors, provides indications that this base may be incorporated into lipids not only by net synthesis pathway, but also by base-exchange reaction.
Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism, 1986
The role that phosphatidylcholine biosynthesis plays in the assembly and secretion of lipoproteins has been investigated in rat hepatocytes, since phosphatidylcholine is the major phospholipid in all serum lipoproteins. Phosphatidylcholine in rat hepatocytes can be made via the CDPcholine pathway or by the methylation of phosphatidylethanolamine. A specific inhibitor of cellular transmethylation, 3-deazaadenosine (10 PM), has been incubated with rat hepatocytes, and we have shown that the biosynthesis of phosphatidylcholine via the methylation of phosphatidylethanolamine derived from ethanolamine was inhibited by greater than 95%. However, incubation of 3-deazaadenosine with cultured rat hepatocytes for up to 18 h did not affect the secretion of any of the apoproteins into VLDL, LDL, HDL fractions or a fraction with density greater than 1.18 g/ml (albumin was the major protein). Nor was there any effect by 3-deazaadenosine on the amount of phosphatidylcholine secreted into the culture medium or into VLDL or HDL. After 18 h the amount of phosphatidylethanolamine that accumulated in the cells was doubled by treatment with 3-deazaadenosine, and the amount of phosphatidylethanolamine secreted into the medium was increased by approximately 70%. It is thus apparent that the synthesis of phosphatidylcholine from ethanolamine is not required for lipoprotein secretion by rat hepatocytes.
Biosynthesis of Rat Brain Phosphatidylcholines from Intracerebrally Injected CHOLINE1
Journal of Neurochemistry, 1976
Ab~tract-[Me-~H]Choline was injected intracerebrally into male rats and the brains immediately removed by particular procedures at regular intervals over the first 1200 s. The incorporation of radioactivity into brain phosphorylcholine, CDP-choline and phosphatidylcholines was examined and quantitated, in order to investigate the relative roles of net synthesis and base-exchange reactions for choline incorporation into lipid. The molecular subspecies of phosphatidylcholines were also examined after isotope administration. Phosphorylcholine, CDP-choline and phosphatidylcholines all became labelled as early as 5 s after the administration of labelled choline. The time course of incorporation of choline into brain lipid is biphasic with two flex points at about 20 and 120 s from the injection. The specific radioactivity of different phosphatidylcholines appears to be different at early and later intervals from injection. The suggestion is made that the base-exchange pathway for choline incorporation into lipid might be operative in viw in early periods after administration. ' This work has been aided by a research grant from the Consiglio Nazionale delle Richerche, Rome (Contract n. 74.00259).
Biosynthesis of Rat Brain Phosphatidylcholines from Intracerebrally Injected Choline
Journal of Neurochemistry, 1976
Ab~tract-[Me-~H]Choline was injected intracerebrally into male rats and the brains immediately removed by particular procedures at regular intervals over the first 1200 s. The incorporation of radioactivity into brain phosphorylcholine, CDP-choline and phosphatidylcholines was examined and quantitated, in order to investigate the relative roles of net synthesis and base-exchange reactions for choline incorporation into lipid. The molecular subspecies of phosphatidylcholines were also examined after isotope administration. Phosphorylcholine, CDP-choline and phosphatidylcholines all became labelled as early as 5 s after the administration of labelled choline. The time course of incorporation of choline into brain lipid is biphasic with two flex points at about 20 and 120 s from the injection. The specific radioactivity of different phosphatidylcholines appears to be different at early and later intervals from injection. The suggestion is made that the base-exchange pathway for choline incorporation into lipid might be operative in viw in early periods after administration. GAIT1 A., DE MEDIO G. E., BRUNETTI M., AMADUCCI L.
The Journal of biological chemistry, 1992
Madin Darby canine kidney (MDCK) cells convert 1-O-[3H]alkyl-2-acyl-sn-glycero-3-phosphocholine [( 3H]alkylacylGPC) to a product tentatively identified as an ethanolamine-containing phosphoglyceride (PE) (Daniel, L. W., Waite, B. M., and Wykle, R. L. (1986) J. Biol. Chem. 261, 9128-9132). In the present study, analysis of the radiolabeled phosphoglycerides as diradylglycerobenzoate derivatives indicated that [3H] alkylacylGPC was initially converted to 1-O-[3H]alkyl-2-acyl-sn-glycero-3-phosphoethanolamine [( 3H]alkylacylGPE) which was subsequently desaturated to 1-O-[3H]alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine [( 3H]alkenylacylGPE). The conversion of [3H]/[32P]alkyl-lysoGPC to [3H]alkenylacylGPE indicated that base exchange enzymes were not involved in this pathway. A phosphono analog of alkyl-lysoGPC, resistant to phospholipase D hydrolysis and radiolabeled in the 1-O-alkyl chain was readily incorporated, acylated, and subsequently metabolized to [3H]alkylacylGPC and...
Journal of Biological Chemistry
Phospholipid synthesis was investigated in human Y79 retinoblastoma cells, a cultured cell line of retinal origin that retains many neural characteristics. Ethanolamine is taken up by Y79 cells through a highaffinity transport system and is utilized to synthesize ethanolamine and choline phosphoglycerides. High-affinity ethanolamine uptake has a K', of 40.6 MM and a Vkof 1.06 nmol/min/mg protein, and the process is Na+ dependent. Choline is the only compound tested that reduced ethanolamine uptake, and very high choline concentrations were required to produce this effect. The cells incorporate ethanolamine into phosphatidylethanolamine and ethanolamine plasmalogen at equivalent rates, and the rates of catabolism of these phospholipids are similar. Only a small quantity of ethanolamine is incorporated into phosphatidylcholine, but the amount is not reduced by the addition of choline. Serine is incorporated into phosphatidylserine, which then is converted to phosphatidylethanolamine. Ethanolamine reduces but does not abolish this conversion. Unlike ethanolamine, only a small amount of serine is incorporated into ethanolamine plasmalogen. It is possible that the ethanolamine high-affinity uptake system is necessary to provide a neural cell with enough free ethanolamine for ethanolamine plasmalogen synthesis.