Metabolism Of Phosphatidylglycerol Research Articles

SlHSP17.7 Ameliorates Chilling Stress-Induced Damage by Regulating Phosphatidylglycerol Metabolism and Calcium Signal in Tomato Plants

Tomatoes (Solanum lycopersicum L.) are sensitive to chilling temperatures between 0 °C and 12 °C owing to their tropical origin. SlHSP17.7, a cytoplasmic heat shock protein, interacts with cation/calcium exchanger 1-like (SlCCX1-like) protein and promotes chilling tolerance in tomato fruits (Zhang, et al., Plant Sci., 2020, 298, 1–12). The overexpression of SlHSP17.7 can also promote cold tolerance in tomato plants, but its specific mechanism remains unclear. In this study, we show that the overexpression of SlHSP17.7 in tomato plants enhances chilling tolerance with better activity of photosystem II (PSII). Metabolic analyses revealed that SlHSP17.7 improved membrane fluidity by raising the levels of polyunsaturated fatty acids. Transcriptome analyses showed that SlHSP17.7 activated Ca2+ signaling and induced the expression of C-repeat binding factor (CBF) genes, which in turn inhibited the production of reactive oxygen species (ROS). The gene coexpression network analysis showed that SlHSP17.7 is coexpressed with SlMED26b. SlMED26b silencing significantly lowered OE-HSP17.7 plants’ chilling tolerance. Thus, SlHSP17.7 modulates tolerance to chilling via both membrane fluidity and Ca2+-mediated CBF pathway in tomato plants.

Synthesis of Phosphatidyl Glycerol Containing Unsymmetric Acyl Chains Using H-Phosphonate Methodology.

Naturally occurring phospholipids, such as phosphatidyl glycerol (PG), are gaining interest due to the roles they play in disease mechanisms. To elucidate the metabolism of PG, an optically pure material is required, but this is unfortunately not commercially available. Our previous PG synthesis route utilized phosphoramidite methodology that addressed issues surrounding fatty acid substrate scope and glycerol backbone modifications prior to headgroup phosphorylation, but faltered in the reproducibility of the overall pathway due to purification challenges. Herein, we present a robust pathway to optically pure PG in fewer steps, utilizing H-phosphonates that features a chromatographically friendly and stable triethyl ammonium H-phosphonate salt. Our route is also amendable to the simultaneous installation of different acyl chains, either saturated or unsaturated, on the glycerol backbone.

Thematic Review Series: Glycerolipids. Cardiolipin synthesis for the assembly of bacterial and mitochondrial membranes

In this article, the formation of prokaryotic and eukaryotic cardiolipin is reviewed in light of its biological function. I begin with a detailed account of the structure of cardiolipin, its stereochemistry, and the resulting physical properties, and I present structural analogs of cardiolipin that occur in some organisms. Then I continue to discuss i) the de novo formation of cardiolipin, ii) its acyl remodeling, iii) the assembly of cardiolipin into biological membranes, and iv) the degradation of cardiolipin, which may be involved in apoptosis and mitochondrial fusion. Thus, this article covers the entire metabolic cycle of this unique phospholipid. It is shown that mitochondria produce cardiolipin species with a high degree of structural uniformity and molecular symmetry, among which there is often a dominant form with four identical acyl chains. The subsequent assembly of cardiolipin into functional membranes is largely unknown, but the analysis of crystal structures of membrane proteins has revealed a first glimpse into the underlying principles of cardiolipin-protein interactions. Disturbances of cardiolipin metabolism are crucial in the pathophysiology of human Barth syndrome and perhaps also play a role in diabetes and ischemic heart disease.

ABCA3 inactivation in mice causes respiratory failure, loss of pulmonary surfactant, and depletion of lung phosphatidylglycerol

The highly branched mammalian lung relies on surfactant, a mixture of phospholipids, cholesterol, and hydrophobic proteins, to reduce intraalveolar surface tension and prevent lung collapse. Human mutations in the ABCA3 transporter have been associated with childhood respiratory disease of variable severity and onset. Here, we report the generation of Abca3 null mice, which became lethargic and cyanotic and died within 1 h of birth. Tissue blots found ABCA3 expression was highest in lung but was also detectable in other tissues, including the kidney. Gross development of kidney and lung was normal in neonatal Abca3(-/-) pups, but the mice failed to inflate their lungs, leading to death from atelectatic respiratory failure. Ultrastructural analysis of the Abca3(-/-) lungs revealed an absence of surfactant from the alveolar space and a profound loss of mature lamellar bodies, the intracellular storage organelle for surfactant. Mass spectrometry measurement of >300 phospholipids in lung tissue taken from Abca3(-/-) mice showed a dramatic reduction of phosphatidylglycerol (PG) levels as well as selective reductions in phosphatidylcholine species containing short acyl chains. These results establish a requirement of ABCA3 for lamellar body formation and pulmonary surfactant secretion and suggest a unique and critical role for the transporter in the metabolism of pulmonary PG. They also demonstrate the utility of the Abca3 null mouse as a model for a devastating human disease.

Metabolism of phosphatidylglycerol by alveolar macrophages in vitro.

In whole animal studies, it has been shown that turnover of surfactant dipalmitoylphosphatidylglycerol (DPPG) is faster than that of dipalmitoylphosphatidylcholine (DPPC). The goal of this investigation was to characterize the metabolism of DPPG by alveolar macrophages and to determine whether they contribute to the faster alveolar clearance of DPPG. Isolated rat alveolar macrophages were incubated with liposomes colabeled with [(3)H]DPPG and [(14)C]DPPC. Macrophages internalized both lipids in a time- and temperature-dependent manner. The uptake of both lipids was increased by surfactant protein (SP) A and by adherence of the macrophages to plastic slides. The isotope ratio of DPPC to DPPG internalized by macrophages in suspension in the absence of SP-A was significantly lower than the isotope ratio in liposomes, suggesting that macrophages preferentially internalize DPPG when SP-A is absent. Phospholipase activity in macrophage homogenate was higher toward sn-2-labeled DPPG than toward sn-2-labeled DPPC. These studies show that alveolar macrophages play an important role in catabolizing surfactant lipids and may be partially responsible for the relatively faster clearance of DPPG from the lung.

Mutants of Chlamydomonas reinhardtii affected in phosphatidylglycerol metabolism and thylakoid biogenesis

Four mutants of Chlamydomonas reinhardtii have been isolated. The mf1 and mf2 strains are not photosynthetically active because they lack PSII activity; they are also devoid of Δ 3- trans-hexadecenoic acid-containing phosphatidylglycerol, and are almost unable to form trimeric LHC2 or develop thylakoid appressions. Seventy-seven K fluorescence emission spectra have shown that mf1 and mf2 mutants are unable to perform significant state transition and are blocked in a permanent state II. The photosynthetic Pmf1 and Pmf2 strains were respectively selected from mf1 and mf2 mutants grown on a minimal medium. Compared to wild type cells, the Pmf1 mutant had about 5 % of Δ 3- trans-hexadecenoic acid-containing phosphatidylglycerol, a weak oxygen evolution activity, the capacity to form low amounts of trimeric LHC2 and a significant level of membrane stacking. A similar partial restoration of the wild type phenotype was observed in the Pmf2 mutant, but to a larger extent: the recovery of about 50 % of Δ 3- trans-hexadecenoic acid-containing phosphatidylglycerol is correlated with the recovery of about 50 % of PSII activity, large amounts of trimeric LHC2 and stacking of photosynthetic membranes. These results demonstrate a clear correspondence between the level of Δ 3- trans-hexadecenoic acid-containing phosphatidylglycerol, the formation of the trimeric LHC2 and the development of grana stacks. The direct involvement of this lipid in these characteristics was demonstrated by the restoration of trimeric LHC2, appressed thylakoids and state I/state II transitions in mf1 and mf2 mutants after in vivo selective targeting of Δ 3- trans-hexadecenoic acid-containing phosphatidylglycerol in their photosynthetic membranes.

Peculiarities of phosphatidylglycerol metabolism in lung tumors

Peculiarities of phosphatidylglycerol metabolism in lung tumors

Metabolism of phosphatidylglycerol and bis(monoacylglycero)-phosphate in macrophage subcellular fractions.

Bis(monoacylglycero)phosphate (BMP) is synthesized from exogenous phosphatidylglycerol (PG) by macrophages (Cochran, F. R., Roddick, V. L., Connor, J. R., Thornburg, J. T., and Waite, M. (1987) J. Immunol. 138, 1877-1883). Previous work from our laboratory showed that arachidonic acid in BMP was released by the macrophages upon challenge of the cells with PMA (Cochran, F. R., Connor, J. R., Roddick, V. L., and Waite, M. (1985) Biochem. Biophys. Res. Commun. 130, 800-806). Here we extend those studies using a model cultured cell line of macrophages, RAW 264.7. When PG labeled with 32P- and [3H]glycerol in both moieties was added to the culture medium, 32P/[3H]BMP was synthesized in a time-dependent manner. Fractionation of cell homogenates on a discontinuous sucrose gradient in which the light membranes were floated from dense sucrose showed an enrichment of [3H]BMP in light membrane fractions. The precursor [3H]PG was also found in the light fractions but, relative to the [3H]BMP, was more abundant in the denser membrane fractions. The appearance of [3H]PG and [3H]BMP in the light membrane fraction was time-dependent which suggested that the initial uptake and metabolism of [3H]PG was into the denser membranes. Incubation of the light membranes under conditions that are optimal for the lysosomal phospholipase A1 led to significant metabolism of [3H]PG. Both degradation of [3H]PG to water-soluble compounds and its conversion to acylphosphatidylglycerol occurred while no lyso-PG was detected. On the other hand, little BMP was found to be degraded. From these studies we postulate that in lysosomes acylphosphatidylglycerol is a precursor of BMP and that the previously reported turnover of arachidonic acid by BMP may occur via transacylation rather than hydrolysis.

Products of phosphatidylglycerol turnover in two Bacillus strains with and without lipoteichoic acid in the cells

In order to understand the phosphatidylglycerol turnover mechanism, especially the differential turnover of diacylated and unacylated glycerol moieties of the lipid, products of phosphatidylglycerol metabolism were surveyed in vivo in Bacillus subtilis W23 and an alkalophile, Bacillus sp. strain A007. When cells of B. subtilis W23 labeled with radioactive glycerol were chased, lipoteichoic acid accumulated 90% of the radioactivity lost from the unacylated glycerol moiety of phosphatidylglycerol. Also, lipids other that phosphatidylglycerol, except diacylglycerol, and glycerol and glycerophosphate incorporated much less radioactivity. The [ 32P]phosphoryl group was also transferred from phosphatidylglycerol to lipoteichoic acid almost quantitatively in B. subtilis W23. A unique metabolism of phosphatidylglycerol was found in Bacillus sp. strain A007 which lacked phosphoglycolipid and lipoteichoic acid, that is, the turnover of phosphatidylglycerol of this organism was less extensive compared with that of B. subtilis W23, and both glycerol moieties of the lipid were metabolized at an identical rate. These results suggested that the major reaction involved in the turnover of phosphatidylglycerol was the transfer of glycerophosphate residue to lipoteichoic acid in a bacterium which possessed lipoteichoic acid and that several minor reactions also were involved in phosphatidylglycerol turnover.

Molecular requirements for B-lymphocyte activation by Escherichia coli lipopolysaccharide.

Certain Escherichia coli mutants altered in phosphatidylglycerol metabolism accumulate fatty acyl derivatives of glucosamine 1-phosphate. Especially prominent is 2,3-diacylglucosamine 1-phosphate (previously designated lipid X), which may be an early precursor of lipid A. We have examined the activity of lipid X (Mr = 711.9) and several related compounds as mitogens towards mouse lymphocytes. As judged by labeling with [methyl-3H]thymidine, lipid X is mitogenic, and it mimics the properties of lipopolysaccharide and lipid A. The following evidence suggests that lipid X exerts its effects by a route similar to that of lipopolysaccharide: (i) lymphocytes from C3H/HeJ mice, which are unresponsive to lipopolysaccharide, are also not stimulated by lipid X; (ii) polymyxin B abrogates lymphocyte stimulation by lipid X; and (iii) lipid X induces the proliferation and maturation of lymphocytes to antibody-producing plaque-forming cells. Selective removal of the ester-linked hydroxymyristate moiety at position 3 totally abolishes mitogenic activity. Other phospholipids, such as phosphatidic acid, CDP-diglyceride, phosphatidylcholine, and lysophosphatidylcholine, have no activity as mitogens. If lipid X and lipid A induce by common mechanism(s) B-lymphocyte proliferation, then it follows from structural comparison that the reducing-end subunit of lipid A is the minimal structural requirement for this activity. Because the structure of lipid X is completely defined, biochemical and pharmacological dissection of B-cell activation by lipopolysaccharide should now be possible.

Effects of chloroquine and 4,4'-bis(diethylaminoethoxy)α,β-diethyldiphenylethane on the incorporation of [ 3H]glycerol into the phospholipids of rat liver lysosomes and other subcellular fractions, in vivo

Oral treatment of rats with 100 mg/kg chloroquine or 4,4'-bis(diethylaminoethoxy)α,β-diethyldiphenylethane for one week causes phospholipid storage in liver and other tissues. The mechanism of this drug-induced lipidosis is not fully understood although several hypotheses have been advanced. In these studies [1,3- 3H]glycerol was injected intravenously into control rats and into chloroquine and 4,4'-bis(diethylaminoethoxy)α,β-diethyldiphenylethane-treated rats. The [ 3H]glycerol was incorporated into phospholipids by de novo synthesis in liver microsomes and transferred to other intracellular membranes which lack the capacity for de novo synthesis of phospholipids. Liver microsomes, mitochondria and lysosomes were isolated and the incorporation of [ 3H]glycerol into phosphoglycerides was determined as a function of time. Treatment with chloroquine or 4,4'-bis(diethylaminoethoxy)α,β-diethyldiphenylethane results in greatly enhanced incorporation of [ 3H]glycerol into lysosomal phospholipids in spite of the fact that the incorporation of [ 3H]glycerol into microsomal phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol by de novo synthesis is reduced. Phosphatidylglycerol, a precursor of lysosomal bis(monoacylglycerol)phosphate, is labeled at a greatly increased rate, especially in liver microsomes from chloroquine- or 4,4'-bis(diethylaminoethoxy)α,β-diethyldiphenylethane-treated rats, while the incorporation of [ 3H]glycerol into phosphatidylinositol in microsomes is reduced. Since both phosphatidylinositol and phosphatidylglycerol are formed from CDP-diacylglycerol, the enhanced incorporation of [ 3H]-glycerol into phosphatidylglycerol cannot be due only to inhibition of phosphatidate phosphohydrolase by these two cationic amphiphilic agents suggesting the possibility of a specific effect of these drugs on phosphatidylglycerol metabolism in liver. [ 3H]Glycerol incorporation into bis(monoacylglycero)phosphate is found only in lysosomes in agreement with our earlier observations. The results suggest increased transfer of newly-synthesized microsomal phospholipids to lysosomes and/or decreased lysosomal catabolism of phospholipids in chloroquine- and 4,4'-bis(diethylaminoethoxy)α,β-diethyldiphenylethane-treated rat liver. Incorporation of newly-formed 3H-labeled phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol into mitochondria is not increased, indicating that a non-specific increase in intracellular phospholipid exchange is not responsible for our observations.

Effect of CO2 concentration on phosphatidylcholine and phosphatidylglycerol metabolism in surfactant and residual lung fractions

An investigation of the effect of change of total CO(2) concentration from 7 to 43 mM at pH 7.35 in the medium perfusing isolated rat lungs on [U-(14)C]glucose incorporation into lung phospholipids has been carried out. The incorporation of [U-(14)C]glucose into phosphatidylcholine and phosphatidylglycerol of the surfactant fraction and of the remaining lung tissue (residual fraction) was observed. Increased CO(2) concentration increased [U-(14)C]glucose incorporation into phosphatidylcholine of the surfactant fraction and residual fraction by 43 and 50%, respectively, during a 2 hr perfusion. Likewise, incorporation of [U-(14)C]glucose into phosphatidylglycerol was increased 22 and 34% into the surfactant and residual fractions, respectively. The percentage of [U-(14)C]glucose incorporated into the fatty acid moieties of phosphatidylcholine of both fractions increased as a result of increased CO(2) concentration. The increase in the incorporation of [U-(14)C]glucose into the fatty acid moieties of phosphatidylcholine was confirmed by an average increase of 56 and 77% in the specific activity of palmitic acid isolated from phosphatidylcholine of the surfactant and residual fraction, respectively, as a result of increased CO(2) concentration. The results suggest that alteration in extracellular CO(2) concentration affects the de novo synthesis from glucose of phosphatidylcholine and phosphatidylglycerol of the surfactant-lipoprotein fraction of lung.

Metabolism of phosphatidylglycerol in cell-free extracts of Escherichia coli.

Cell-free extracts from Escherichia coli strain number 9, lacking among other enzymes glycerol kinase, are able to incorporate [2-3H] glycerol into phospholipids. The characteristics of this incorporation indicate that it is not taking place through the regular glycerol phosphate pathway of phospholipid synthesis which occurs when this compound is used as a precursor or even when extracts of E. coli strain 7, having a functional glycerol kinase, are incubated with [2-3H] glycerol. In E. coli strain 9 extracts glycerol is exclusively incorporated into the distal position of phosphatidyl-glycerol while in the other strains the middle position glycerol is partially labelled.

Analyse et métabolisme des phospholipides du cœur. Incorporation in vivo de 32P-orthophosphate dans les lipides cardiaques du rat

Heart phospholipid metabolism was studied by intraperitoneal injection of 32 P-orthophosphate to the rat. Phospholipids were separated by silicic acid column chromatography and bidimensional thin-layer chromatography on silicagel. Phosphatidylcholine, phosphatidylethanolamine and diphosphatidylglycerol are the major phospholipid constitutents of the heart, we noted also the presence of phosphatidylglycerol and the low level of sphingomyelin. Our technique was particularly suitable for the separation of phosphatidylserine and phosphatidylinositol. Our technique was particularly suitable for the separation of phosphatidylserine and and 14 hours), showed a strong incorporation into phosphatidylinositol, phosphatidylcholine and phosphatidylglycerol. Sphingomyelin, phosphatidylethanolamine and diphosphatidylglycerol had, in contrary, very low specific activities even after 14 hours. Studying their different fatty acid composition and their different specific activities we try to explain the metabolism of phosphatidylglycerol and its conversion into diphosphatidylglycerol in rat heart. Le métabolisme des phospholipides du cœur est étudié après injection de 32 P-orthophosphate chez le rat. Les phospholipides sont séparés par chromatographie sur colonne d'acide silicique et sur couche mince de silicagel par chromatographie uni ou bidimensionnelle. Ces techniques nous permettent de confirmer la prépondérance des phosphatidylcholines, des phosphatidyléthanolamines et du diphosphatidylglycérol, le taux faible des sphingomyélines et la présence de phosphatidylglycérol. Elles nous permettent également d'obtenir une bonne séparation des phosphatidylsérines et des phosphatidylinositols. Les activités spécifiques des phospholipides, mesurées en fonction du temps (4, 6, 8 et 14 heures après l'injection de l'isotope) montrent une forte incorporation dans les phosphatidylinositols, les phosphatidylcholines et le phosphatidylglycérol. Sphingomyélines, phosphatidyléthanolamines et diphosphatidylglycérol, montrent au contraire, des activités spécifiques faibles même au bout de 14 heures. A la lumière de leur composition en acides gras, et de leurs activités spécifiques nettement différentes nous essayons d'expliquer le métabolisme du phosphatidylglycérol et sa conversion en diphosphatidylglycérol dans le cœur de rat.

Metabolism of phosphatidylglycerol, phosphatidylethanolamine, and cardiolipin of Bacillus stearothermophilus.

The total phospholipid content of Bacillus stearothermophilus was constant during exponential growth, increased during the transition from the exponential to stationary phase of growth, and then slowly increased during the stationary phase. The first increase was a result of an increase in phosphatidylethanolamine; the second was a result of an increase in cardiolipin. Cessation of aeration of an exponentially growing culture or suspension in a nongrowth medium resulted in an immediate reduction in the rate of total phospholipid and phosphatidylethanolamine synthesis and a quantitative conversion of phosphatidylglycerol to cardiolipin. Cardiolipin appeared to be synthesized by the direct conversion of two molecules of phosphatidylglycerol to cardiolipin. After a 20-min pulse of (32)P, phosphatidylglycerol showed the most rapid loss of (32)P followed by cardiolipin, whereas phosphatidylethanolamine did not lose (32)P. The loss of (32)P from the total lipid pool, phosphatidylglycerol, and cardiolipin was biphasic, with rapid loss during the first two bacterial doublings followed by a greatly reduced rate of loss. The major loss of (32)P from the total phospholipid pool appeared to be by breakdown of cardiolipin. The loss of (32)P from the lipid pool was energy dependent (i.e., did not occur under anaerobic conditions or in the absence of an energy source) and was dependent on some factor other than the concentration of cardiolipin in the cells. The apparent conversion of phosphatidylglycerol to cardiolipin was independent of energy metabolism. Chloramphenicol reduced the rate of turnover of both phosphatidylglycerol and cardiolipin. The rate of lipid synthesis (all phospholipid components) was constant for about 10 min after the addition of chloramphenicol but diminished markedly after 20 min. Turnover of (32)P incorporated into phospholipid during a 30-min period prior to the addition of chloramphenicol was more rapid after the removal of chloramphenicol than that of (32)P incorporated during a 30-min period in the presence of chloramphenicol.

Correlation between metabolism of phosphatidylglycerol and membrane synthesis in Escherichia coli

A functional relation between phosphatidylglycerol metabolism and biological events in the cytoplasmic membrane were studied. The author measured the loss of radioactivity from phosphatidylglycerol during synchronous growth in Escherichia coli K12 and found that it took place in a stepwise manner at a specific cell phase, the middle phase of cell division. It was also demonstrated that cytochrome b 1 which is localized predominantly in the cytoplasmic membrane was increased in discrete steps and that active transport of l-α-glycerophosphate was multiplied in a similar fashion. These increases coincided exactly with the time of loss of radioactivity of phosphatidylglycerol. Furthermore discontinuous appearances could also be observed in a culture in which cell division is synchronized but DNA synthesis is not. The evidence that these phenomena occur simultaneously in or on a membrane matrix, strongly suggests a correlation between the disappearance of phosphatidylglycerol and the synthesis of the membrane constituents, or the formation of functionally active membrane components. Phospholipids and cellular packed volume were increased throughout the cell cycle. The existence of two modes of synthesis of membrane constituents was suggested from these results, in one of which the synthesis is coupled with the loss of radioactivity of phosphatidylglycerol, and the other in which membrane constituents are synthesized in whole cell cycle.

Altered phospholipid metabolism in a sodium-sensitive mutant of Escherichia coli.

A mutant of Escherichia coli has been isolated, the growth of which is inhibited by low concentrations (1 mm) of NaCl. High levels of magnesium, calcium, or strontium in the medium permit growth in the presence of sodium. The metal content of the inhibited mutant is normal, but the strain is unable to tolerate levels of sodium to which the wild type is indifferent. Immediately after the addition of sodium to cultures of the mutant, rates of synthesis of protein, ribonucleic acid, deoxyribonucleic acid, and total lipid are unchanged, but more cardiolipin and less phosphatidylethanolamine are produced. The direct enzymatic cause of this change, which affects membrane function, is not known. Studies of the metabolism of phosphatidylglycerol in vivo after pulse-labeling with [2-(3)H]glycerol reveal that a major pathway both in wild-type and mutant strains involves the cleavage of labeled glycerol from phosphatidylglycerol.

Detection of a rapidly metabolizing portion of the membrane cardiolipin in Haemophilus parainfluenzae.

Heterogeneity in the metabolism of cardiolipin (CL) has been detected in Haemophilus parainfluenzae. Pulse-chase experiments showed that a portion of the total CL incorporated and then lost (32)P much more rapidly than the rest of the CL in the cells. The metabolism of each phosphate of the CL differed. The phosphate of the phosphatidyl glycerol (PG) portion of the CL had a more active metabolism than the phosphate of the phosphatidic acid portion of the molecule. Only a portion of the PG pool contributed to the formation of CL. Ethylenediaminetetraacetic acid inhibited the CL-specific phospholipase D in vitro and, when added to growing cells, resulted in more rapid PG metabolism, suggesting that CL hydrolysis contributed to the PG pool.

Microbial assimilation of hydrocarbons: phospholipid metabolism.

An analysis of the turnover of the major phospholipids of Micrococcus cerificans growing or nongrowing cultures. The turnover rates of (14)C-PE and (14)C-PE were 61.5% of the total phospholipid, exhibited no significant rate of turnover in either growing or nongrowing cultures. The turnover rates of PE-(14)C and PE-(32)P were 3.2% per hr and 1.2% per hr, respectively. Phosphatidylglycerol (PG) exhibited a turnover rate of 11% and 7.7% per hr for (14)C and (32)P, respectively, indicating an extremely slow metabolism. PG metabolism was examined in greater detail, and the data indicated a preferential 75% incorporation of glycerol-1,3-(14)C into the unacylated portion of the PG molecule. The turnover of cardiolipin (CL) was extremely slow in growing cells whereas nongrowing cells exhibited a 30% and 36% increase per hr for (14)C-Cl and (14)C-CL, respectively. Glycerol-1,3-(14)C was not converted to phospholipid fatty acid carbon; all radioactivity appeared only in the water-soluble backbone of the phospholipids. The kinetics of assimilation of hexadecane-1-(14)C into cellular lipids is presented. Radioactivity in neutral lipid increased approximately sevenfold over the growth cycle, whereas radioactivity in phospholipid increased 50-fold during the same time period. The incorporation of radioactive fatty acids derived from the direct oxidation of hexadecane-1-(14)C demonstrated differential kinetics of assimilation into PE, PG, and CL. The results indicated a rapid turnover of phospholipid fatty acids in M. cerificans growing at the expense of hexadecane.

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.