Turnover Of Phosphatidylethanolamine Research Articles

Phospholipid dynamics in ex vivo lung cancer and normal lung explants

In cancer cells, metabolic pathways are reprogrammed to promote cell proliferation and growth. While the rewiring of central biosynthetic pathways is being extensively studied, the dynamics of phospholipids in cancer cells are still poorly understood. In our study, we sought to evaluate de novo biosynthesis of glycerophospholipids (GPLs) in ex vivo lung cancer explants and corresponding normal lung tissue from six patients by utilizing a stable isotopic labeling approach. Incorporation of fully 13C-labeled glucose into the backbone of phosphatidylethanolamine (PE), phosphatidylcholine (PC), and phosphatidylinositol (PI) was analyzed by liquid chromatography/mass spectrometry. Lung cancer tissue showed significantly elevated isotopic enrichment within the glycerol backbone of PE, normalized to its incorporation into PI, compared to that in normal lung tissue; however, the size of the PE pool normalized to the size of the PI pool was smaller in tumor tissue. These findings indicate enhanced PE turnover in lung cancer tissue. Elevated biosynthesis of PE in lung cancer tissue was supported by enhanced expression of the PE biosynthesis genes ETNK2 and EPT1 and decreased expression of the PC and PI biosynthesis genes CHPT1 and CDS2, respectively, in different subtypes of lung cancer in publicly available datasets. Our study demonstrates that incorporation of glucose-derived carbons into the glycerol backbone of GPLs can be monitored to study phospholipid dynamics in tumor explants and shows that PE turnover is elevated in lung cancer tissue compared to normal lung tissue.

Deletion of the 2-acyl-glycerophosphoethanolamine cycle improve glucose metabolism in Escherichia coli strains employed for overproduction of aromatic compounds.

BackgroundAs a metabolic engineering tool, an adaptive laboratory evolution (ALE) experiment was performed to increase the specific growth rate (µ) in an Escherichia coli strain lacking PTS, originally engineered to increase the availability of intracellular phosphoenolpyruvate and redirect to the aromatic biosynthesis pathway. As result, several evolved strains increased their growth fitness on glucose as the only carbon source. Two of these clones isolated at 120 and 200 h during the experiment, increased their μ by 338 and 373 %, respectively, compared to the predecessor PB11 strain. The genome sequence and analysis of the genetic changes of these two strains (PB12 and PB13) allowed for the identification of a novel strategy to enhance carbon utilization to overcome the absence of the major glucose transport system.ResultsGenome sequencing data of evolved strains revealed the deletion of chromosomal region of 10,328 pb and two punctual non-synonymous mutations in the dhaM and glpT genes, which occurred prior to their divergence during the early stages of the evolutionary process. Deleted genes related to increased fitness in the evolved strains are rppH, aas, lplT and galR. Furthermore, the loss of mutH, which was also lost during the deletion event, caused a 200-fold increase in the mutation rate.ConclusionsDuring the ALE experiment, both PB12 and PB13 strains lost the galR and rppH genes, allowing the utilization of an alternative glucose transport system and allowed enhanced mRNA half-life of many genes involved in the glycolytic pathway resulting in an increment in the μ of these derivatives. Finally, we demonstrated the deletion of the aas-lplT operon, which codes for the main components of the phosphatidylethanolamine turnover metabolism increased the further fitness and glucose uptake in these evolved strains by stimulating the phospholipid degradation pathway. This is an alternative mechanism to its regeneration from 2-acyl-glycerophosphoethanolamine, whose utilization improved carbon metabolism likely by the elimination of a futile cycle under certain metabolic conditions. The origin and widespread occurrence of a mutated population during the ALE indicates a strong stress condition present in strains lacking PTS and the plasticity of this bacterium that allows it to overcome hostile conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-015-0382-6) contains supplementary material, which is available to authorized users.

Alterations in Phospholipid Catabolism in Mycobacterium Tuberculosis LysX Mutant

Mycobacterium tuberculosis lysX mutant, defective for production of lysinylated phosphatidylglycerol, is sensitive to cationic antimicrobial peptides, is not proficient for proliferation in mice lungs, and exhibits altered membrane potential (Maloney et al., 2009). In the present study we show that a lysX complement strain expressing lysX from inducible tet promoter is proficient in restoring lysX phenotypes, confirming that the observed phenotypes are specific to lysX. To evaluate the correlation between changes in membrane potential and lysX activity, we visualized regions of cardiolipin (CL), one of the abundant phospholipids of mycobacteria, by staining with fluorescent dye 10-N-nonyl acridine orange and found that CL is localized as bright spots at septal regions and poles of actively dividing cells, but not in stationary phase cells. lysX mutants were elongated and showed more numerous and brighter CL staining at both mid cell and quarter cell septa, compared with wild type, indicating a defect in the cell division process. Evaluation of 14C-acetic acid incorporation into major phospholipids such as CL, phosphatidylethanolamine (PE), phosphatidylinositol (PI), and their degradation between lysX mutant and its parent revealed differences in the turnover of PE and PI. Our results favor a hypothesis that alterations in phospholipid metabolism could be contributing to changes in membrane potential, hence the observed phenotype of lysX mutant.

13C-labeled 18:2n-6 recovered in brush border membrane phospholipids short time after administration

The purpose of the present study was to examine the short-term effect of dietary specific structured triacylglycerols (MLM, M = 8:0, L = 18:2n-6), LLL and MMM on the fatty acid composition of brush border membrane (BBM) phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Rats were administered intragastrically a bolus of ML*M, M*LM*, L*L*L* or M*M*M* (* = 13C-labeled fatty acid). Rats were decapitated 2 hours and 6 hours later, and the fatty acid composition and 13C-enrichment of BBM-PC and -PE were determined. 13C-enriched 18:2n-6 was observed in BBM-PC after intragastric administration of L*L*L* and ML*M, whereas no 13C-labeled fatty acids were recovered after administration of M*LM* or M*M*M*. Interestingly, no 13C-labeled fatty acids were detected in the BBM-PE fraction. This could be due to a lower turnover of PE than PC and to a different ratio of saturated and unsaturated fatty acids in the two phospholipid pools. Minor effects on BBM-PC and BBM-PE fatty acid profiles (mole-%) were observed. The present study demonstrated for the first time incorporation of 13C-labeled 18:2n-6 into BBM-PC 2 hours and 6 hours after intragastric administration of L*L*L* or ML*M. This emphasizes the influence of the dietary fatty acid on BBM fatty acid composition and the rapid incorporation of dietary long-chain fatty acids into intestinal enterocyte phospholipids. Medium-chain fatty acids in a single meal exert only a minor influence on the BBM phospholipid fatty acid profile.

Phosphatidylethanolamine derived from phosphatidylserine is deacylated and reacylated in rat hepatocytes

The metabolism of phosphatidylserine (PS), Phosphatidylethanolamine (PE) and phosphatidylcholine (PC), derived from [ 3H]serine, has been studied in rat hepatocytes. After an initial pulse with radioactivity for 10 min and a chase for up to 240 min, cells were harvested and PS, PE and PC isolated. At the end of the pulse, greater than 90% of [ 3H]serine derived phospholipid radioactivity was associated with PS. In the subsequent chase, newly-made PS was degraded rapidly with less than 25% of the label lost from PS appearing in the PE and PC pools. In contrast, [ 3H]serine-labeled PE turnover was not detectable. Very little newly-made PS was converted to PC. PE and PC were further fractionated into molecular species by high-performance liquid chromatography. We report that [ 3H]serine-labeled PE is deacylated/reacylated with the major product of remodeling being 18:0–20:4 PE. In contrast, [ 3H]serine-labeled PC is not significantly remodeled.

Anoxic injury accelerates phosphatidylcholine degradation in cultured cardiac myocytes by phospholipase C

In neonatal cultured cardiac myocytes under normoxic conditions, 32P i incorporation pattern into various phospholipids, and double-labeling experiments with 32P i and [ 3H]methyl choline, suggest that phosphatidylcholine atid phosphatidylinositol are turned over rapidly, whereas the turnover of phosphatidylethanolamine is probably much slower. While increased levels of the corresponding lysophospholipids were not found under anoxia, release of diacylgycerol and phosphorylcholine was observed. These data strongly suggest that phospholipase C, and not phospholipase A 2, is involved in phospholipid degradation in cultured cardiomyocytes under anoxic conditions.

Lipid bilayer in genetic hypertension.

Membrane microviscosity, phospholipid composition, and turnover were measured in cultured vascular smooth muscle cells isolated from mesenteric arteries of stroke-prone spontaneously hypertensive and age-matched, normotensive Wistar-Kyoto rats. Membrane microviscosity, measured with fluorescence polarization, revealed greater microviscosity (lower fluidity) of the membranes isolated from smooth muscle cells from hypertensive as compared with those isolated from normotensive rats (p less than 0.01). Preincubation of membranes from hypertensive rats with 5 mM calcium reduced membrane microviscosity in "core" and in "surface" regions of the bilayer toward values observed in Wistar-Kyoto rats. Phospholipid composition did not differ between intact aortas and cultured mesenteric cells or between those tissues obtained from normotensive and from hypertensive rats. The total lipid-associated radioactivity was significantly lower in cells from stroke-prone spontaneously hypertensive rats than in those from Wistar-Kyoto controls (p less than 0.01). Phosphatidylcholine incorporated 70% and phosphatidylinositol 16% of total lipid-associated radioactivity, with no difference between cells from hypertensive and normotensive animals. Turnover of phosphatidylethanolamine was greater in cells from Wistar-Kyoto rats (p = 0.02), whereas turnover of phosphatidylserine was greater in cells from stroke-prone spontaneously hypertensive rats (p = 0.04). The greater microviscosity of the lipid bilayer in hypertension is a generalized defect of the matrix in which the transport proteins function. We hypothesize that this defect is responsible for the multiple abnormalities of membrane transport systems that have been described in genetic hypertension.

Phorbol ester-stimulated hydrolysis of phosphatidylcholine and phosphatidylethanolamine by phospholipase D in HeLa cells. Evidence that the basal turnover of phosphoglycerides does not involve phospholipase D.

12-O-Tetradecanoylphorbol-13-acetate (TPA) stimulated the release of [3H]ethanolamine from HeLa cells prelabeled with [3H]ethanolamine within 2 min, and of [3H]choline from cells prelabeled with [3H]choline after a lag of 10-20 min. This result suggests that TPA activates phospholipase D. Propranolol alone or propranolol plus TPA stimulated phosphatidic acid (PA) labeling in cells prelabeled with [3H]hexadecanol. In the presence of ethanol, TPA stimulated the accumulation of labeled phosphatidylethanol (PEth); no PEth was formed in the absence of TPA. TPA-dependent PEth accumulation was not observed in cells pretreated with TPA to down-regulate protein kinase C, whereas propranolol-induced accumulation of PA was unaffected by TPA pretreatment. Incubation of prelabeled cells with propranolol alone caused a rapid loss of label and phospholipid mass from both phosphatidylethanolamine and phosphatidylcholine (PC) together with an accumulation of PA and phosphatidylinositol plus phosphatidylserine. When [3H]hexadecanol-prelabeled cells were pulse labeled with 32P to label nucleotide pools, propranolol induced the accumulation of both 3H- and 32P-labeled PA. When cells were prelabeled with lyso-PC double labeled with 3H and 32P, and incubated with propranolol, only 3H-labeled PA accumulated, indicating that the pathways involved in the basal turnover of PC resulted in the loss of 32P from the lipid. These results suggest that the basal turnover of phosphatidylethanolamine and PC involves the sequential actions of phospholipase C, diglyceride kinase, and PA phosphohydrolase.

A soluble fatty acyl – acyl carrier protein synthetase from the bioluminescent bacterium Vibrio harveyi

An enzyme catalyzing the ligation of long chain fatty acids to bacterial acyl carrier protein (ACP) has been detected and partially characterized in cell extracts of the bioluminescent bacterium Vibrio harveyi. Acyl-ACP synthetase activity (optimal pH 7.5-8.0) required millimolar concentrations of ATP and Mg2+ and was slightly activated by Ca2+, but was inhibited at high ionic strength and by Triton X-100. ACP from either Escherichia coli (apparent Km = 20 microM) or V. harveyi was used as a substrate. Of the [14C]fatty acids tested as substrates (8-18 carbons), a preference for fatty acids less than or equal to 14 carbons in length was observed. Vibrio harveyi acyl-ACP synthetase appears to be a soluble hydrophilic enzyme on the basis of subcellular fractionation and Triton X-114 phase partition assay. The enzyme was not coinduced with luciferase activity or light emission in vivo during the late exponential growth phase in liquid culture. Acyl-ACP synthetase activity was also detected in extracts from the luminescent bacterium Vibrio fischeri, but not Photobacterium phosphoreum. The cytosolic nature and enzymatic properties of V. harveyi acyl-ACP synthetase indicate that it may have a different physiological role than the membrane-bound activity of E. coli, which has been implicated in phosphatidylethanolamine turnover. Acyl-ACP synthetase activity in V. harveyi could be involved in the intracellular activation and elongation of exogenous fatty acids that occurs in this species or in the reactivation of free myristic acid generated by luciferase.

Phosphatidylethanolamine turnover is an early event in the response of NB2 lymphoma cells to prolactin

The effect of prolactin on phospholipid metabolism in the prolactin-dependent rat lymphoma cell line Nb2 was investigated in cells prelabeled with [3H]arachidonic acid or [3H]ethanolamine. Prolactin (20 ng/ml) caused (a) a 20-60% loss of radiolabeled phosphatidylethanolamine within 0.5 to 2 min, (b) a loss of [3H]ethanolamine-labeled phosphatidylethanolamine from crude membranes, (c) a rapid accumulation of [3H]phosphoethanolamine and [3H]ethanolamine, and (d) a transient increase (15 s to 2 min) in prostaglandin F2 alpha and E2. Arachidonic acid (1-2 micrograms/ml) induced Nb2 cell growth but prostaglandin F2 alpha, E2, ethanolamine, and phosphoethanolamine did not. Prostaglandin E2 inhibited while prostaglandin F2 alpha enhanced growth in the presence of prolactin or arachidonic acid. These results suggest that stimulation of Nb2 cell growth by prolactin is linked to activation of a phosphatidylethanolamine-specific phospholipase C. Arachidonic acid and prostaglandin F2 alpha may participate in regulating the mitogenic action of prolactin.

Prostaglandin synthesis linked to phosphatidylinositol turnover in isolated rat glomeruli

Prostaglandins produced by the glomerulus are important factors in controlling glomerular function. The controlling step, i.e., the release of arachidonic acid from the phospholipids by either phospholipase A 2 and/or C, remains poorly defined. The present studies were designed to determine which factors control arachidonic acid turnover and prostaglandin synthesis in glomeruli. As tools we used the calcium ionophore A23187, mepacrine, a phospholipase inhibitor, trifluoperazine, a calmodulin antagonist, and angiotensin II. A23187 (2 μM) caused a significant stimulation of both prostaglandin E 2 and prostaglandin F 2α synthesis (measured by radioimmunoassay), which was associated with increased phosphatidylinositol turnover (measured by [ 14C]arachidonic acid and [ 32P]orthophosphate incorporation). Surprisingly, trifluoperazine (10–100 μM) also progressively increased synthesis of both prostaglandins, which was accompanied by increased phosphatidic acid/phosphatidylinositol turnover and decreased phosphatidylinositol content. In contrast, phosphatidylcholine and phosphatidylethanolamine turnover were significantly inhibited by trifluoperazine and their total content remained unaffected. Mepacrine (1 mM) decreased prostaglandin synthesis and both phosphatidylcholine and phosphatidylethanolamine turnover, and had no consistent effect on phosphatidylinositol turnover in control glomeruli. Mepacrine did, however, inhibit both A23187 or trifluoperazine-induced increase in phosphatidylinositol turnover. Angiotensin II increased turnover of phosphatidylinositol and also phosphatidylcholine, as determined by incorporation of [ 14C]arachidonic acid. Thus, all agents that increased prostaglandin synthesis also enhanced phosphatidylinositol turnover. The exact pathway of arachidonic acid release remains to be determined.

Turn-over of phospholipids in Selenomonas ruminantium.

The particulate enzyme prepared from Selenomonas ruminantium subsp. lactilytica catalyzed the formation of phosphatidylserine (PS) from CDP-diglyceride and serine, and phosphatidylethanolamine (PE) from PS. This indicates that PS and PE in this organism are synthesized through a similar pathway to that in Escherichia coli. In turn-over experiments with [32P]orthophosphate and [14C]caproate, a rapid turn-over of PE was observed, while ethanolamine plasmalogen was relatively stable. The decrease of 14C-radioactivity in PE side-chains was accompanied by an increase of 14C-radioactivity in side-chains of ethanolamine plasmalogen. In pulse label-chase experiments with [32P]orthophosphate, significant amounts of 32P-radioactivities were incorporated into plasmalogens at the beginning of the chase and a precursor product relationship was observed between serine plasmalogen and ethanolamine plasmalogen. On the contrary, in pulse-label-chase experiments using [14C]caproate and [3H]glycerol, no significant radioactivity was incorporated into plasmalogens at the beginning of the chase and radioactivities in plasmalogens slowly increased during the chase. These results indicate that 1-O-alk-1'-enyl-2-acyl-glycerol moieties of plasmalogens are derived from a large precursor pool, but the phosphorous moiety is not. This concept was supported by the fact that synthesis of plasmalogens occurred in the absence of fatty acid synthesis. We wish to propose the possibility that 1-O-alk-1'-enyl-2-acyl-glycerol moieties of plasmalogens are derived from the diglyceride moieties of diacyl phospholipids.

Phospholipid turnover during phagocytosis in human polymorphonuclear leucocytes

We have previously observed that the phagocytosis of zymosan particles coated with complement by human polymorphonuclear leucocytes is accompanied by a time- and dose-dependent inhibition of phosphatidylcholine synthesis by transmethylation [García Gil, Alonso, Sánchez Crespo & Mato (1981) Biochem. Biophys. Res. Commun.101, 740-748]. The present studies show that phosphatidylcholine synthesis by a cholinephosphotransferase reaction is enhanced, up to 3-fold, during phagocytosis by polymorphonuclear cells. This effect was tested by both measuring the incorporation of radioactivity into phosphatidylcholine in cells labelled with [Me-(14)C]choline, and by assaying the activity of CDP-choline:diacylglycerol cholinephosphotransferase. The time course of CDP-choline:diacylglycerol cholinephosphotransferase activation by zymosan mirrors the inhibition of phospholipid methyltransferase activity previously reported. The extent of incorporation of radioactivity into phosphatidylcholine induced by various doses of zymosan correlates with the physiological response of the cells to this stimulus. This effect was specific for phosphatidylcholine, and phosphatidyl-ethanolamine turnover was not affected by zymosan. The purpose of this enhanced phosphatidylcholine synthesis is not to provide phospholipid molecules rich in arachidonic acid. The present studies show that about 80% of the arachidonic acid generated in response to zymosan derives from phosphatidylinositol. A transient accumulation of arachidonoyldiacylglycerol has also been observed, which indicates that a phospholipase C is responsible, at least in part, for the generation of arachidonic acid. Finally, isobutylmethylxanthine and quinacrine, inhibitors of phosphatidylinositol turnover, inhibit both arachidonic acid generation and phagocytosis, indicating a function for this pathway during this process.

Metabolism of phosphatidylethanolamine in the frog retina

The synthesis and the turnover of phosphatidylethanolamine in frog retinal rod outer segments and microsomes were studied by monitoring the incorporation of five radioactive precursors: 32PO 4, 33PO 4, [ 3H]glycerol, [ 3H]serine, and [ 3H]ethanolamine. 1. 1. Labeled serine was actively incorporated into phosphatidylethanolamine. The kinetics of the labeling patterns in both microsomes and rod outer segments was consistent with formation via decarboxylation of phosphatidyl-serine. 2. 2. Ethanolamine was found, to be an ineffective precursor of phosphatidylethanolamine, suggesting that the major pathway for phosphatidylethanolamine synthesis in the retina is via the decarboxylation reaction. 3. 3. An active methylation of phosphatidylethanolamine to phosphatidylcholine was observed in both retinal microsomes and rod outer segments. 4. 4. The kinetics of labeling of phosphatidylethanolamine in the rod outer segments was different for the various isotopic precursors, and was found to depend on the relative turnover times of the precursor pools. Glycerol was the only precursor that gave a true pulse of radioactivity. 5. 5. The specific activity of phosphatidylethanolamine derived from labeled glycerol declined exponentially, demonstrating that the labeled lipid was diffusely distributed throughout the rod outer segments. The half-life of phosphatidylethanolamine in the rod outer segments was determined to be 18 days. Comparison of this value to the turnover time of rod outer segment integral proteins revealed that rod outer segment lipid is renewed at a faster rate than protein.

Turnover of lipid components in liver microsomes, mitochondria and plasma membrane of 6-, 12- and 24-month old rats

The turnover of lipid was examined in the livers of 6-, 12- and 24-month old rats. Heterogeneity of turnover was noted for each membrane fraction. The lipid turnover rate was highest in 12-month old rats and was the same in 6- and 24-month old rats. The higher rate of lipid turover at 12 months was observed in both the neutral and polar lipid components of the liver membranes. In the polar lipid fractions isolated from the microsomal and mitochondrial membranes the increase in lipid turnover rate at 12 months was related to increase in the turnover of phosphatidylethanolamine.

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.

Altered phospholipid metabolism in a temperature-sensitive mutant of a thermophilic bacillus

The phospholipid metabolism of a temperature-sensitive mutant of a thermophilic bacillus was studied after the shift from a permissive (58 degrees C) to a restrictive (65 degrees C) growth temperature. During the short period of growth of the mutant at 65 degrees C, the proportions of cardiolipin and its 3-acyl derivative (lyso-cardiolipin) increased, and the proportions of phosphatidylglycerol and phosphatidylethanolamine decreased on cell dry weight basis. In 32P incorporation and turnover experiments, phosphatidylglycerol showed the most rapid uptake and loss of the label. Turnover of cardiolipin, limited to a short period, ceased 18 min after the shift, as did the turnover of phosphatidylethanolamine. In the absence of net phospholipid synthesis, there was a quantitative conversion of phosphatidylglycerol to cardiolipin and an increase in the proportion of lyso-cardiolipin. Chloramphenicol, added to the medium at the time of the shift, reduced the rate of phospholipid synthesis, prevented the increase in the proportions of cardiolipin and lyso-cardiolipin, and slowed the decrease in the proportions of the other two phospholipids. The results indicated a defect in the regulatory mechanism(s) of phospholipid metabolism in the mutant at the restrictive temperature.

Phospholipase a activity in growing Eacherichia coli cells

The turnover of phosphoglycerides in Escherichia coli B, B fad and K 19 was investigated under normal growth conditions. E. coli B fad displayed appreciable turnover of phosphatidylethanolamine and polyglycerophosphatides. During growth, this strain released phospholipids, lipopolysaccharide material and proteins including phospholipase A to the medium and produced sizeable amounts of free fatty acids due mainly to phosphatidylethanolamine hydrolysis. The two other strains displayed little or no turnover of phosphatidylethanolamine and a lower production of free fatty acid: however polyglycerophosphatide breakdown in this case was similar to that of strain B fad. Also E. coli B and K 19 had a more rigid cell envelope structure than B fad as could be assessed by the tendency to release outer membrane materials to the medium and susceptibility to lysis. The results suggested that the levels of phospholipase A activity in various strains of growing E. coli is related to the integrity of the cell envelope.

Effect of shift-down and growth inhibition on phospholipid metabolism of Escherichia coli.

The metabolism of phospholipids of Escherichia coli was studied under conditions which inhibit various metabolic processes. Phospholipid synthesis and turnover were not inhibited by growth-inhibitory amounts of various antibiotics. Turnover of phosphatidylglycerol (PG) was inhibited by small amounts of dinitrophenol and by anaerobiosis. Turnover of phosphatidylethanolamine (PE), which is not detected in control cultures, was demonstrated under conditions of incipient lysis. When cells were shifted down from a rich to a poor medium, PE synthesis was inhibited, and incorporation of glycerol into the distal position of PG was stimulated. Under these conditions, turnover of the phosphate and the acylated glycerol moieties of PG was inhibited. Increased synthesis of PE was detected when filamentous cells were induced to make septa. The results indicate that PE synthesis is related to growth and cell division, whereas PG metabolism is related to other cell processes.

Phospholipid metabolism in escherichia coli after a shift in temperature

Phospholipid metabolism was determined quantitatively during a 5-h lag period in growth after changing the temperature of a culture of exponentially growing Eschenchia coli B from 37° to 10°. The results obtained were as follows. 1. 1. The phospholipid content increased about 20%. 2. 2. The amount of vaccenic acid increased 2-fold, while the amounts of other fatty acids in the phospholipid fraction changed relatively little. 3. 3. At least 33% of the phosphodiester moiety of phospholipids was degraded to water-soluble products and about 54% more phosphodiester moiety was synthesized from P i in the medium and intracellular precursors, as revealed by 32P-incorporation and chase experiments. 4. 4. There was turnover of phosphatidyl ethanolamine, a compound which is known to be very stable in normally growing cells of E. coli, as well as of phosphatidyl glycerol or cardiolipin. 5. 5. The fatty acyl moiety of lipids was not degraded, but maintained as fatty acids or fatty acyl esters. It was also shown that the fatty acyl moiety of the neutral lipid fraction, including free fatty acids, was actively reutilized for phospholipid synthesis. These results were discussed in relation to enzymes which had been found in vitro.