Phosphatidylethanolamine Biosynthesis Research Articles

The effects of temperature on the fatty acid and phospholipid composition of four obligately psychrophilicVibrio Spp.

The free fatty acid and phospholipid composition of 4 psychrophilic marineVibrio spp. have been determined in chemostat culture with glucose as the limiting substrate over a temperature range 0–20°C. All the isolates show maximum glucose and lactose uptake at 0°C and this correlates with maximum cell yield. None of the isolates contain fatty acids with a chain length exceeding 17 carbon atoms.Vibrio AF-1 andVibrio AM-1 respond to decreased growth temperatures by synthesizing increased proportions of unsaturated fatty acids (C15:1, C16:1 and C17:1) whereas inVibrio BM-2 the fatty acids undergo chain length shortening. The fourth isolate (Vibrio BM-4) contains high levels (60%) of hexadecenoic acid at all growth temperatures and the fatty acid composition changes little with decreasing temperature. The principal phospholipid components of the four psychrophilic vibrios were phosphatidylserine, phosphatidylglycerol, phosphatidylethanolamine and diphosphatidylglycerol. Lyso-phosphatidylethanolamine and 2 unknown phospholipids were additionally found inVibrio AF-1. The most profound effect of temperature on the phospholipid composition of these organisms was the marked increase in the total quantities synthesized at 0°C. At 15°C phosphatidylglycerol accumulated in the isolates as diphosphatidylglycerol levels decreased. Additionally inVibrio BM-2 andVibro BM-4 phosphatidylserine accumulates as phosphatidylethanolamine biosynthesis was similarly impaired. The observed changes in fatty acid and phospholipid composition in these organisms at 0°C may explain how solute transport is maintained at low temperature.

Pulmonary lung and surfactant lipid biosynthesis in dogs under septic and hypovolemic shock syndromes

1. 1. The incorporation of [ 14C]glycerol 3-phosphate and [ 3H]palmitate into different classes of lipids from lung tissue and surfactant was studied by perfusing dog heart-lung preparations after the onset of various shock syndromes. 2. 2. Patterns of isotope incorporation into free fatty acids, phosphatidylcholine and phosphatidylethanolamine of lung tissue and surfactant from animals under hypovolemic shock did not show any significant alteration. 3. 3. However, septic shock syndrome was able to influence largely the biosynthesis of phosphatidylethanolamine and, particularly, of phosphatidycholine. The relative contribution of different pathways of biosynthesis of lecithins showed by the control lung tissue was distorted in the septic lung. 4. 4. This fact influences the presence and the function of lecithins in the pulmonary surfactant under endotoxic shock.

Selective changes in microsomal enzymes of triacylglycerol phosphatidylcholine, and phosphatidylethanolamine biosynthesis during differentiation of 3T3-L1 preadipocytes.

Selective changes in microsomal enzymes of triacylglycerol phosphatidylcholine, and phosphatidylethanolamine biosynthesis during differentiation of 3T3-L1 preadipocytes.

Evidence that biosynthesis of phosphatidylethanolamine, phosphatidylcholine, and triacylglycerol occurs on the cytoplasmic side of microsomal vesicles.

Experiments were performed to localize the hepatic microsomal enzymes of phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol biosynthesis to the cytoplasmic or lumenal surface of microsomal vesicles. Greater than 90 percent of the activities of fatty acid-CoA ligase (EC 6.2.1.3), sn-glycerol 3-phosphate acyltransferase (EC 2.3.1.15), lysophosphatidic acid acyltransferase, diacylglycerol acyltransferase (EC 2.3.1.20), diacylglycerol cholinephosphotransferase (EC 2.7.8.2), and diacylglycerol ethanolaminephosphotransferase (EC 2.7.8.1) was inactivated by proteolysis of intact microsomal vesicles. The phosphatidic acid phosphatase (EC 3.1.3.4) was not inactivated by any of the protease tested. Under conditions employed, <5 percent of the luminal mannose-6-phosphatase (EC 3.1.3.9) activity was lost. After microsomal integrity was disrupted with detergents, protease treatment resulted in a loss of >74 percent of the mannose-6-phosphatase activity. The latency of the mannose-6-phosphatase activity was not affected by protease treatment. Mannose-6-phosphatase latency was not decreased by the presence of the assay components of several of the lipid biosynthetic activities, indicating that those components did not disrupt the microsomal vesicles. None of the lipid biosynthetic activities appeared latent. The presence of a protease-sensitive component of these biosynthetic activities on the cytoplasmic surface of microsomal vesicles, and the absence of latency for any of these biosynthetic activities suggest that the biosynthesis of phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol occurs asymmetrically on the cytoplasmic surface of the endoplasmic reticulum. The location of biosynthetic activities within the transverse plane of the endoplasmic reticulum is of particular interest for enzymes whose products may be either secreted or retained within the cell. Phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol account for the vast majority of hepatic glycerolipid biosynthesis. The phospholipids are utilized for hepatic membrane biogenesis and for the formation of lipoproteins, and the triacylglycerols are incorporated into lipoproteins or accumulate within the hepatocyte in certain disease states (14). The enzymes responsible for the biosynthesis of these glycerolipids (Scheme I) from fatty acids and glycerol-3P have all been localized to the microsomal subcellular fraction (12, 16, 29, 30). Microsomes are derived from the endoplasmic reticulum and are sealed vesicles which maintain proper sidedness. (11, 22). The external surface of these vesicles corresponds to the cytoplasmic surface of the endoplasmic reticulum. Macromolecules destined for secretion must pass into the lumen of the endoplasmic reticulum (5, 23). Uncharged molecules of up to approximately 600 daltons are able to enter the lumen of rat liver microsomes, but macromolecules and charged molecules of low molecular weight do not cross the vesicle membrane (10, 11). Because proteases neither cross the microsomal membrane nor destroy the permeability barrier of the microsomal vesicles, only the enzymes and proteins located on the cytoplasmic surface of microsomal vesicles are susceptible to proteolysis unless membrane integrity is disrupted (10, 11). By use of this approach, several enzymes and proteins have been localized in the transverse plane of microsomal membranes (11). With the possible exception of cytochrome P 450, all of the enzymes and proteins investigated were localized asymmetrically by the proteolysis technique (11). By studies of this type, as well as by product localization, glucose-6-phosphate (EC 3.1.3.9) has been localized to the luminal surface of microsomal vesicles (11) and of the endoplasmic reticulum (18, 19). All microsomal vesicles contain glucose-6-phosphatase (18, 19) which can effectively utilize mannose-6-P as a substrate, provided the permeability barrier of the vesicles has been disrupted to allow the substrate access to the active site located on the lumenal surface (4). An exact correspondence between mannose- 6-phosphate activity and membrane permeability to EDTA has been established (4). The latency of mannose-6-phosphatase activity provides a quantitative index of microsomal integrity (4.) Few of the microsomal enzymes in the synthesis of phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol have been solubilized and/or purified, and little is known about the topography of these enzymes in the transverse or lateral planes of the endoplasmic reticulum. An asymmetric location of these biosynthetic enzymes on the cytoplasmic or lumenal surface of microsomal vesicles may provide a mechanism for regulation of the glycerolipids to be retained or secreted by the cell, and for the biogenesis of asymmetric phospholipid bilayers. In this paper, we report investigations on the localization of all seven microsomal enzymes (Scheme I) in the biosynthesis of triacylglycerol, phosphatidylcholine, and phosphatidylethanolamine, using the protease technique with mannose-6-phosphatase serving as luminal control activity. The latency of these lipid biosynthetic enzymes was also investigated, using the latency of mannose-6-phosphatase as an index of microsomal integrity.

Identification of bound pyruvate essential for the activity of phosphatidylserine decarboxylase of Escherichia coli.

Phosphatidylserine decarboxylase, an intrinsic membrane protein of Escherichia coli, catalyzes the decarboxylation of phosphatidylserine, the final step in the biosynthesis of phosphatidylethanolamine, the principal membrane lipid of this organism. The purified enzyme lacks the absorption spectrum characteristic of pyridoxal-containing enzymes, and it has now been found to contain bound pyruvate, the carbonyl function of which is essential for catalytic activity. The decarboxylase is inactivated by treatment with a number of reagents that attack carbonyl groups, including sodium borohydride. Reduction with tritiated borohydride leads to the introduction of stably bound radioactivity, which, after acid hydrolysis, has been identified as tritiated lactate by several chromatographic procedures and by treatment with lactate dehydrogenase. The enzyme resists inactivation by cyanoborohydride in the absence of substrate, but is readily inactivated by this reagent in the presence of phosphatidylserine. Under the conditions of treatment of neutral pH, cyanoborohydride does not react with carbonyl residues at an appreciable rate, but reduces imino groups much more rapidly. This finding, together with demonstrated dependence of the enzyme upon the carbonyl residue of pyruvate for activity, strongly suggests that a Schiff base is formed by addition of the amino group of phosphatidylserine to the pyruvate residue of the enzyme as an essential step in the action of the decarboxylase.

Inhibition of rat liver CDPethanolamine: 1,2-diacylglycerol ethanolamine-phosphotransferase activity by ATP and pantothenic acid derivatives.

The properties of rat liver microsomal CDPethanolamine: 1,2-diacylglycerol ethanolamine-phosphotransferase (ethanolaminephosphotransferase; EC 2.7.8.1) are studied with respect to metal ion and substrate concentration. The enzyme requires magnesium (20 mM) or manganese (1 mM) ions for optimum activity. Manganese ions are better activators of ethanolaminephosphotransferase activity than are magnesium ions. Calcium 1 mM) inhibits the magnesium-activated ethanolaminephosphotransferase by 86% and the manganese-activated enzyme by 57%. The Km for CDPethanolamine is 2.4 and 0.7 x 10(-4) M, in the presence of magnesium or manganese ions, respectively. ATP plus pantetheine significantly inhibit the manganese-activated ethanolaminephosphotransferase, while the magnesium-activated enzyme is inhibited by ATP plus pantetheine and slightly stimulated by ATP plus CoA. In the presence of either metal ion, ATP itself inhibits enzyme activity, while CoA or pantetheine when added alone have no effect. Evidence is presented indicating that the inhibition of ethanolaminephosphotransferase activity by ATP plus CoA or ATP plus pantetheine is not due to the formation of acyl-CoA or acyl-S-pantetheine esters. At the present time, however, the true mechanism of inhibition is unknown. The results indicate that the cellular levels of ATP, CoA, pantetheine, magnesium, manganese, and calcium ions may all play a role in the regulation of phosphatidylethanolamine biosynthesis.

Biosynthesis of phosphatidylethanolamine from CDP-ethanolamine by the Golgi complex of rat liver in vitro

A Golgi-rich fraction from rat liver has been shown to synthesize phosphatidylethanolamine from CDP-ethanolamine in vitro. The implications of the existence of such a pathway for the membrane flow hypothesis are discussed.

Role of Mitochondria and Divalent Cations in the Regulation of Phosphatidyicholine and Phosphatidylethanolamine Biosynthesis by a Microsomes-Cell Supernatant Fraction of Rat Liver1

Role of Mitochondria and Divalent Cations in the Regulation of Phosphatidyicholine and Phosphatidylethanolamine Biosynthesis by a Microsomes-Cell Supernatant Fraction of Rat Liver1

Rapid transmembrane movement of newly synthesized phospholipids during membrane assembly.

The transbilayer distribution of phospholipids in Bacillus megaterium is asymmetrical, with twice as much phosphatidylethanolamine internally as externally (Rothaman, J. E. & Kennedy, E. P. (1977) J. Mol. Biol. 110,603-618). We now report that the biosynthesis of phosphatidylethanolamine is also asymmetrical. Newly synthesized phosphatidylethanolamine was found first on the cytoplasmic side of the membrane of pulse-labeled cells and later was redistributed until the specific radioactivity of the outer face became equal to that of the inner face of the bilayer. The rate of transmembrane movement is at least 30,000 times faster than the rate of spontaneous diffusion (flip-flop) of phosphatidylethanolamine across artificial phospholipid bilayers, indicating that transmembrane movement must be a facilitated process in living cells, perhaps involving membrane proteins.

Biosynthesis of rat brain phosphatidylethanolamines from intracerebrally injected ethanolamine

[2- 3H]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.

Phosphatidate Phosphohydrolase and the Regulation of Glycerolipid Biosynthesis

Phosphatidate is an intermediate in the biosynthesis of diacylglycerol, triacylglycerol, phosphatidylethanolamine, phosphatidylcholine and CDP-diacylglycerol. In addition, phosphatidate may be subject to degradation by particulate phospholipases. The factors regulating the disposition of phosphatidate have interested numerous investigators. We have studied the reactions of phosphatidate metabolism in several tissues and under various environmental conditions. Phosphatidate phosphohydrolase activity is found primarily in the microsomal and supernatant fractions of liver, adipose tissue and intestine. Presumably the physiologically important substrate for this reaction is the particulate-bound phosphatidate and methods for the preparation of this substrate have been developed (Fallon et al., 1975). Radioactively labelled phosphatidate bound to microsomal particles is prepared from sn-[1 ,3-14C]glycerol 3-phosphate. A wide range of microsomal phosphatidate concentrations may be prepared by this technique, although the usual microsomal concentration is approx. 5 nmol/mg of microsomal protein. This substrate has been used in most of our studies of phosphatidate phosphohydrolase, CDP-diacylglycerol formation and phospholipase A. There are several lines of evidence which support an important role for phosphatidate phosphohydrolase in the regulation of neutral-lipid formation by liver or adipose-tissue particulate preparations. (1) The reaction rate of phosphatidate phosphohydrolase under optimum conditions in vitro is the lowest in the overall synthetic pathway in liver microsomal fractions (Lamb & Fallon, 1974a). The rate of phosphohydrolase activity was determined as 0.6-0.8 nmol/min per mg of microsomal protein when radiolabelled particulate-bound phosphatidate was used as substrate. The overall rate of glycerolipid formation by these microsomal preparations was approx. l.Onmol/min per mg of microsomal protein. The optimum rate of microsomal sn-glycerol 3-phosphate acyltransferase was 5-7-fold higher. In the presence of added rat liver supernatant fraction the rate of microsomal phosphatidate phosphohydrolase is increased 5-20-fold. However, at ratios of microsomal protein to supernatant protein estimated for the intact cell, the increase in phosphohydrolase activity is much more modest. (2) Induction of increased liver triacylglycerol formation by administration of a high-fructose diet is accompanied by an equivalent rise in the activity of the phosphohydrolase, as shown in Table 1. These changes in lipid metabolism occur simultaneously over a 10-day period (Lamb & Fallon, 19746). Further, the phosphatidate content of liver microsomal preparation is diminished by approx. 15 %, and diacylglycerol increased by approx. 90 % under these dietary conditions. (3) The increase in liver triacylglycerol content after partial hepatectomy is accompanied by a corresponding increase in phosphatidate phosphohydrolase activity (Mangiapane et al., 1973). (4) Several drugs which cause substantial inhibition of phosphatidate phosphohydrolase activity in vitro also result in inhibition of neutral-lipid formation when administered to the intact animal (Brindley & Bowley, 1975; Lamb et al., 1977). A series of 1,3-bis(substituted phenoxy)-2-propanones inhibited microsomal phosphatidate phosphohydrolase activity as measured in vitro. The inhibition ranged from 8 to 92% total activity. In animals fed on these agents in laboratory chow the incorporation of [14C]glycerol into hepatic triacylglycerol was decreased by 3-75 %. Agents which caused a 50 % or greater decrease in phosphatidate phosphohydrolase activity in vitro also lowered

Inhibition of phosphatidylethanolamine biosynthesis by S‐adenosylmethionine

Inhibition of phosphatidylethanolamine biosynthesis by S‐adenosylmethionine

Phospholipid metabolism in Pseudomonas BAL-31 infected with lipid-containing bacteriophage PM2.

Infection of Pseudomonas BAL-31 with the lipid-containing bacteriophage PM2 resulted in no detectable change in the rate of phosphatidylglycerol (PG) or phosphatidylethanolamine (PE) biosynthesis. An increase in the PG content of infected cultures was not seen until the cultures began to lyse, and this increase was in fact only a relative increase resulting from the extensive turnover of PE at the onset of culture lysis. Turnover studies revealed that the glycerol, phosphorus fatty acid, and ethanolamine moieties of PE turned over simultaneously at the time of lysis, and therefore made it unlikely that there was a PE to PG conversion during the latent period of the phage. The lipid found in the bacteriophage did not reflect a preferential selection for lipid synthesized before or after infection, but in fact reflected the composition of the host membrane at the time the phage were assembled. The use of a modified medium that allowed the cultivation of Pseudomonas BAL-31 as a prototroph and resulted in reliable lysis times of infected cultures led us to the conclusion that PM2 infection effects little change in host phospholipid metabolism, and that there is sufficient PG in the host cytoplasmic membrane to account for a full burst of phage. As a result of the reliable lysis times that we have achieved, we concluded that certain metabolic events, i.e., PE turnover, are lytic phenomena and must not be confused with events relevant to the biosynthesis and maturation of the phage.

Phospholipid biosynthesis in sarcoplasmic reticulum membrane during development

Biosynthesis of phosphatidic acid, phosphatidylcholine and phosphatidylethanolamine in the sarcoplasmic reticulum membrane has been investigated. The results show that sarcoplasmic reticulum, in addition to its main function, i.e. transport and accumulation of Ca 2+, is able to synthetize phospholipids by the same pathways as endoplasmic reticulum of other tissues. The changes of activity of enzymes involved in phospholipid biosynthesis during muscle development have been analysed. The extent of sn-glycero-3-phosphate and lysophosphatidylcholine acylation by acyl-CoA or free fatty acids in the presence of ATP and CoA is the same at every stage of development. The specific activity of glycerolphosphate acyltransferase(s) increases progressively during development up to about the 10th day of postnatal life and then decreases to the adult level. Linoleate esterifies sn-glycero-3-phosphate to a higher extent than palmitate, especially during postnatal period. The main product of sn-glycero-3-phosphate acylation is phosphatidic acid. The specific activity of lysolecithin acyltransferase increases from the low embryonic value to a maximum at about the 3rd day of postnatal life, followed by a decrease to the adult value. The activity of cholinephosphotransferase decreases from a high value observed during the earliest embryonic period studied until the 3rd day before birth, and then begins to increase again from about the 5th day of postnatal life. The activity of ethanolaminephosphotransferase decreases continuously with age. The main product of phosphatidylethanolamine methylation is phosphatidylmonomethylethanolamine. The specific activity of phosphatidylethanolamine methyltransferase increases from the embryonic period to a maximum between the 4th and the 9th day of postnatal life followed by a decrease to the adult value.

Biosynthesis of phosphatidylcholine and phosphatidylethanolamine by germinating soya bean.

Conference Article| February 01 1976 Biosynthesis of Phosphatidylcholine and Phosphatidylethanolamine by Germinating Soya Bean JOHN L. HARWOOD JOHN L. HARWOOD 1Department of Biochemistry, University College, P.O. Box 78, Cardiff CF1 1XL, Wales, U.K. Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1976) 4 (1): 50–52. https://doi.org/10.1042/bst0040050 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation JOHN L. HARWOOD; Biosynthesis of Phosphatidylcholine and Phosphatidylethanolamine by Germinating Soya Bean. Biochem Soc Trans 1 February 1976; 4 (1): 50–52. doi: https://doi.org/10.1042/bst0040050 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 1976 Biochemical Society1976 Article PDF first page preview Close Modal You do not currently have access to this content.

Effect of propylthiouracil-induced hypothyroidism on phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin synthesis in chick liver microsomes.

Biosynthesis of phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin was studied in liver endoplasmic reticulum obtained from newly hatched chicks which were made hypothyroid by feeding 0.2% propylthiouracil. In vitro measurements were made of the specific activities of phosphorylcholine-glyceride (cholinephosphotransferase (EC 2.7.8.2), hosphorylethanolamine-glyceride (ethanolamine-phosphotransferase (EC 2.7.8.1)), and phosphorylcholine-ceramide (ceramide cholinephosphotransferase (EC 2.7.8.3)) transferases in control and hypothyroid chick liver for a period of 40 days. The specific activity of all three transferases began to decline after the chicks were on the propylthiouracil-containing diet for 5 days and steadily declined, reaching levels 10-15% of the controls after 15 days. These low levels were maintained for as long as the chicks were on this diet. Administration of L-thyroxine (15 mug/100 g of body weight) to the hypothyroid chicks caused a marked increase in the specific activities of all three transferases, reaching levels similar to those seen in the control chicks in 36-48 h. The specific activities then declined as the chicks were maintained on the diet of propylthiouracil, reaching the former low levels after 120 h. Administration of cycloheximide alone to the hypothyroid chicks caused a rise in the specific activities of the transferases after 24 h approximately equal to that caused by thyroxine alone, while thyroxine and cycloheximide together were no different than either alone. These studies indicate that in some manner circulating thyroxine controls the activities of enzymes involved in the biosynthesis of phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin in chick liver endoplasmic reticulum. There was no evidence that induction of hypothyroidism by propylthiouracil had any effect on the activities of these enzymes in the CNS.

Conditional lethal phosphatidylserine decarboxylase mutants of Escherichia coli

The final step in the biosynthesis of phosphatidylethanolamine, the major membrane lipid of Escherichia coli, is catalyzed by the membrane-bound enzyme, phosphatidylserine decarboxylase. A variation of a procedure for localized mutagenesis (Hong and Ames, 1971) was employed to generate conditional lethal mutants in phosphatidylserine decarboxylase. In our modification, an episome carrying the psd gene closely linked to purA+ was heavily mutagenized in vivo in a strain also lysogenic for phage P1CMclr100. After induction of a phage lytic cycle, the purA+ marker was transduced to a purA- recipient. A majority of the Pur+ transductants thus contained a psd gene originating from the heavily mutagenized episomal strain. Three mutants were isolated in which temperature-sensitive growth is caused by thermosensitive phosphatidylserine decarboxylase activity that is defective in vivo at the non-permissive temperature. All 3 mutations were mapped at the same location as psd1, being cotransduced with melA, purA, and ampA. The gene order in this region, as determined by a phage Pl-meidated, three-factor cross is ampA-psd-purA. psd+ is dominant to the psd mutant alleles.

Inhibition of Phosphatidylethanolamine Biosynthesis in Baby Hamster Kidney-21 Cells Infected with Semliki Forest Virus

Semliki Forest virus inhibits phosphatidylethanolamine biosynthesis in baby hamster kidney-21 cells 6 h after infection. Viral infection reduced the incorporation of [1,2-14C]-ethanolamine into intact cells by approximately 50%. A similar reduction in the activity of the ethanolaminephosphotransferase (EC 2.7.8.1) was also observed. The apparent Km for CDPethanolamine was 60 muM for the microsomal enzymes from infected or mock-infected cells. In addition, exogenous diglyceride only stimulated by 1.5-fold the ethanolaminephosphotransferase from virus- or mock-infected cells, whereas the same diglyceride preparations stimulated the cholinephosphotransferase (EC 2.7.8.2) from baby hamster kidney cells by sixfold. Generation of endogenous diglyceride by pretreatment of the microsomes with phospholipase C (EC 3.1.4.3) stimulated the activity of the cholinephosphotransferase but not the ethanolaminephosphotranferase. Semliki Forest virus does not inhibit all microsomal enzymes, since the activities of NADH- K3Fe(CN)6 reductase and NADH dehydrogenase (EC 1.6.99.3) were not affected. The ethanolaminephosphotransferase from virus- and mock-infected cells showed similar profiles of activity as a function of temperature; this result and other studies suggest that that membranous environment of the ethanolaminephosphotransferase was not significantly modified by the virus.

Biosynthesis of phosphatidylethanolamines and phosphatidylcholines from ethanolamine and choline in rat liver

1. The kinetics of phosphatidylcholine and phosphatidylethanolamine synthesis in rat liver were followed 5-60 min after the intraportal injection of [14-C]choline and [3-H]-ethanolamine. 2. At all time-intervals the specific radioactivity of CDP-choline was only about half that of phosphorylcholine. This indicated that CDP-choline was formed at a similar rate from phosphorylcholine and phosphatidylcholines, the latter probably through the reverse reaction of cholinephosphotransferase (EC 2.7.8.2.). In view of recent data obtained from experiments in vitro this implies a significant role for the cholinephosphotransferase reaction in the turnover of molecular species of phosphatidylcholine. 3. The specific radioactivity of CDP-ethanolamine was about twice that of phosphorylethanolamine at all time-intervals studied. This supports a previous suggestion that the liver phosphorylethanolamine pool is subject to compartmentation and shows that there is no rapid equilibration between different pools. In contrast with a recent study, no evidence was found for any significant methylation of phosphoryl-or CDP-ethanolamine to the corresponding choline derivative. 4. Quantitative data on the biosynthesis of molecular species of phosphoLIPIDS via CDP derivatives were calculated according to simple kinetic models. They were in the same range as those calculated from earlier data on precusors incorporated via diacylglycerols. 5. The proportion of radioactive phosphatidylethanolamines appearing in the plasma was approximately ten times lower than that for phosphatidylcholines. No selectivity was observed in the transfer into plasma of different molecular species of phosphatidylethanolamine.

Biosynthesis of phosphatidyl ethanolamine in Mycobacterium 607

In Mycobacterium 607 ( M. 607) streptomycin appears to inhibit the formation of phosphatidyl ethanolamine (PE) and polyglycerol phosphatide (PGP), by approximately 35%, as can be seen by 32P incorporation studies. PE is the only phosphatide containing nitrogenous base and is present in pathogenic, nonpathogenic and saprophytic species of mycobacteria. Incorporation of - 14C of ethanolamine-1- 14C into ethanolamine phosphate (EP) and PE, demonstration that, this incorporation is absolutely dependent on the presence of diglyceride (DG) and cytidine triphosphate (CTP), occurrence of the enzymes glycerolkinase and phosphatidic acid phosphatase and the absence of phosphatidyl serine (PS) decarboxylase strongly suggest that, in M. 607 the biosynthesis of PE is accomplished via CDP-ethanolamine mediated pathway.