Turnover Of Phosphatidylglycerol Research Articles

Simultaneous measurement of phosphatidylglycerol and disaturated‐phosphatidylcholine palmitate kinetics from alveolar surfactant. Study in infants with stable isotope tracer, coupled with isotope ratio mass spectrometry

Disaturated-phosphatidylcholine (DSPC) and phosphatidylglycerol (PG) are respectively the first and the third most abundant phospholipid in human alveolar surfactant. Their concentration decreases in airway surfactant of adults and infants with respiratory distress syndrome and cystic fibrosis. In this study, we used mass spectrometry (IRMS) to investigate the turnover of DSPC and PG in tracheal aspirates (TA) obtained from infants with normal or diseased lungs. We studied eight infants requiring mechanical ventilation: two with no lung disease, four with diaphragmatic hernia, one with ATP-binding cassette sub-family A member 3 heterozygote mutation and one with sepsis. Patients received deuterated water for 48 h as metabolic precursors of palmitate-DSPC and palmitate-PG. Serial TAs were obtained every 6 h for five days or until extubation. DSPC and PG were isolated from TA by column and high-performance thin layer chromatography. Deuterium enrichments of palmitate-DSPC and PG residues were measured by IRMS coupled with a gas chromatographer. Median secretion time (ST), peak time (PT) and fractional synthesis rate (FSR) were 3.7 [0.9- 13.4] h, 71.0 [52.2 - 85.2] h and 6.6 [6.3 - 11.1] %/day for DSPC and 19.3 [6.4 - 22.8] h, 49.0 [33.0 - 52.5] h and 5.8 [4.8 - 10.9] %/day for PG. This study shows that it is feasible to use deuterium derived from body water to trace simultaneously airway surfactant DSPC and PG in humans. When compared within the same patient, DSPC and PG had similar fractional synthesis rates, but PG had a shorter PT, suggesting differences in the life cycle of these essential surfactant components.

Diphosphatidylglycerol in experimental acute alveolar injury in the dog.

Acute alveolar injury closely resembling that seen in humans was induced in dogs by subcutaneous injection of N-nitroso-N-methylurethane. Necrosis of alveolar epithelial cells was observed during early injury. Proliferation of immature epithelial cells which began during early injury and became massive after peak injury was followed by their differentiation to mature type II cells during recovery. Quantities of diphosphatidylglycerol (DPG) and of phosphatidylglycerol (PG) in alveolar lavage and in post-lavage lung tissue were measured. An increase in tissue DPG coincided with a sharp decrease in tissue and lavage PG during early injury. DPG was not detectable in the lavage. During late recovery, tissue DPG increased threefold over controls. This increase was accompanied by persistence of a 50% decrease in tissue PG and 83% decrease in lavage PG. Biosynthesis of DPG and PG in isolated lung mitochondria demonstrated that DPG was formed from PG in the presence of CDP-diglyceride. These findings suggest that the low level of PG in the surfactant complex during acute alveolar injury is due to increased turnover of PG to DPG in the lung.

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.

Transfer of the phosphatidyl moiety of phosphatidylglycerol to phosphatidylethanolamine in Escherichia coli

Phosphatidylglycerol was pulse-labeled with radioactive lipid precursors in a serine auxotroph of Escherichia coli. Most of the radioactivity of phosphatidylglycerol labeled in a serine-depleted medium was transferred to phosphatidylethanolamine during a chase in the presence of L-serine, but not in its absence. Metabolism of fatty acyl moieties labeled with [1-14C]acetate, acylated glycerol moieties labeled with [2-3H]glycerol, and phosphate moieties labeled with 32Pi, followed by a chase in the presence of cerulenin, showed that the intact phosphatidyl moiety of phosphatidylglycerol was transferred to phosphatidylethanolamine. The composition of phosphatidylethanolamine molecular species was unaltered and not perturbed by the transfer of the phosphatidyl moiety of phosphatidylglycerol. The increase of phosphatidylethanolamine with a concomitant decrease of phosphatidylglycerol was not coupled with the postulated turnover of phosphatidylglycerol to membrane-derived oligosaccharides and lipoprotein. It is suggested that phosphatidylglycerol is capable of providing its phosphatidyl moiety for the production of phosphatidylethanolamine in response to the relief of serine limitation by addition of L-serine.

Degraded and stable phosphatidylglycerol in Escherichia coli inner and outer membranes, and recycling of fatty acyl residues

The metabolic fate of membrane phospholipids in exponentially growing Escherichia coli was reexamined by incorporation and chase of labeled precursors: [ 32P]phosphate, [2- 3H]glycerol and 3H-labeled fatty acids. It was found that the well-known turnover of phosphatidylglycerol lasted only about two generation times; after which period, the remaining labeled phosphatidylglycerol, approximately one-third of the total, was stable for at least the subsequent two generation times. The location of the stable phosphatidylglycerol pool remaining after the turnover in the outer and inner membrane was investigated. Both envelopes were found to contain stable phosphatidylglycerol so that the existence of a stable portion cannot be ascribed to its exclusive location in one leaflet. In some experiments, a small loss of labeled phosphatidylethanolamine was also observed, and upon fractionation this was found to occur exclusively in the outer membrane. [ 32P]Phosphate and [2- 3H]glycerol labels of the degraded phospholipids were lost from lipid-soluble material, whereas labeled fatty acid, palmitate or oleate was reincorporated into newly synthesized phosphatidylethanolamine and phosphatidylglycerol, so that total fatty acid label remained constant in (membrane) phospholipid during chase. In view of the amount of glycerol lost, the recycling of the fatty acids under the form of diacylglycerols to phosphatidic acid does not appear to be the predominant pathway of reincorporation. After double labeling with [ 32P]phosphate and [ 3H]palmitate, followed by chase, a complete balance sheet of loss and reincorporation of fatty acid, in the three phospholipids, in the two envelopes could be established. Results indicate that fatty acid was reincorporated essentially in the inner membrane phospholipids. Movements of phospholipids and of fatty acids from one membrane to another and in the plane of each layer are discussed in the light of the results.

Studies on the biosynthesis of acylphosphatidylglycerol in Escherichia coli B and B/r

The present study has demonstrated that one molecule of acylphosphatidylglycerol was synthesized from two molecules of phosphatidylglycerol by the transacylation reaction in which phosphatidylglycerol acted both as an acyl donor and an acceptor. Phosphatidylethanolamine was identified as an another acyl donor, participating in acylphosphatidylglycerol formation. These results are discussed in terms of a new pathway for the turnover of phosphatidylglycerol in Escherichia coli.

The inhibition of phospholipid synthesis in Escherichia coli by phenethyl alcohol

The kinetics of lipid metabolism during phenethyl alcohol treatment of Escherichia coli were examined. Phenethyl alcohol at a non-bacteriostatic concentration reduces the accumulation of [ 32P] phosphate into phospholipids and alters the phospholipid composition of the cell membrane. The changes in phospholipid composition are a result of the inhibitory effect of phenethyl alcohol on the rates of synthesis of the individual phospholipids. The inhibition in the rate of phosphatidylethanolamine synthesis by phenethyl alcohol was twice the inhibition in the rate of phosphatidylglycerol synthesis. The de novo rate of cardiolipin synthesis was only slightly inhibited. However, net cardiolipin accumulation increased during phenethyl alcohol treatment due to a more rapid turnover of phosphatidylglycerol to cardiolipin. Phenethyl alcohol also altered the fatty acid composition of the cell as a result of its inhibitory effect on the rate of individual fatty acid synthesis. However, the inhibition of phospholipid synthesis was not reversed by fatty acid supplementation of phenethyl alcohol treated cells. This result indicates that phenethyl alcohol does not inhibit phospholipid synthesis solely at the level of fatty acid synthesis.

The mode of action of polyketoacidomycin on Bacillus subtilis.

The antibiotic action of poly ketoacidomycin (PKAM) on Bacillus subtilis was examined. PKAM stimulated the turnover of phosphatidyl glycerol (PG) to cardiolipin (DPG) and reduced the amounts of the normal fatty acids (nFAs) C-14 and C-16 and anteiso (a) C-17. Addition of bacterial PG to cultures treated with PKAM reduced the effect of the antibiotic.The foregoing changes in lipid composition were associate d with changes in cell permeability . Loss of cellular valine, norvaline and phosphates was observed and a significant decrease in the cellular concentration of Na+ and K+ ions was noted when the test organism was incubate d with PKAM for periods up to 15 minutes. Longer incubation of the bacteria with the antibiotic caused an appreciable increase in RN A content of the cells and a reduction in the DNA and protein content. Polyketoacidomycin (PKAM), first isolated b y SHIMI et al., 1) possesses substantial anti-microbial activity against gram-positive bacteria as well as some gram-negative bacteria. The acid hydrolysate of the antibiotic contains glucose, alanine, and acetone, as well as pyruvic, glyoxylic, α-ketoglutaric, α-ketobutyric and acetoacetic acids.

Metabolism of phospholipids in Bacillus stearothermophilus.

Bacillus stearothermophilus B65 showed two stages of active logarithmic growth on a glucose based medium. Its incorporation of 32PO4 into phospholipids was higher at 55°C than at 37°C. At 37°C phosphatidylglycerol was the major phospholipid but at 55°C it was replaced by cardiolipin. Pulse-chase studies showed that turnover of phosphatidylglycerol and cardiolipin was extensive at certain stages of growth and indicated that phosphatidylglycerol could be the precursor of cardiolipin. Turnover rates at 37°C and at 55°C were similar. The proportion of phosphatidylethanolamine was highest when the pH of the medium was low. This phospholipid was stable at 37°C but at 55°C it might undergo a slow turnover.

Effects of levorphanol on phospholipid metabolism and composition in Escherichia coli

1. 1. The effects of growth inhibitory concentrations of the morphine analogue levorphanol on the metabolism and composition of membrane phospholipids were investigated in Escherichia coli. 2. 2. Incorporation of radioactive precursors into the total lipid fraction is reduced. 3. 3. During incubation with levorphanol there is a gradual rise in the proportion of radioactivity incorporated into cardiolipin, from 5% (untreated) to 55–70% after 60 min. In addition to the more rapid labeling of cardiolipin there is evidence for reduced breakdown of cardiolipin in the presence of levorphanol. 4. 4. The incorporation of precursors into phosphatidyl ethanolamine is markedly reduced. The turnover of phosphatidyl glycerol is accelerated and phosphatidyl ethanolamine, normally stable, exhibits turnover in the presence of levorphanol. 5. 5. After 1 h incubation with levorphanol the relative amounts of individual phospholipids, determined as phospholipid phosphorus, are 45% phosphatidyl ethanolamine, 10% phosphatidyl glycerol and 45% cardiolipin, as compared to 68% phosphatidyl ethanolamine, 25% phosphatidyl glycerol and 7% cardiolipin in untreated bacteria. 6. 6. In drug-free medium the phospholipid labeling pattern of cells labeled in the presence of levorphanol slowly reverts towards normal. 7. 7. Possible relationships between the observed alterations in phospholipid metabolism and composition and the effects of levorphanol on transport and on ribosomal RNA synthesis are discussed.

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.

Formation of a new phosphatidyl glycerol derivative in E. coli

A particulate fraction isolated from E. coli cells was found to convert 14C-labelled phosphatidyl glycerol into an hitherto uncharacterized lipid. Mild alkaline hydrolysis of this lipid yielded glycerophosphorylglycerol as the only product. Detailed chromatographic analysis identified the intact lipid as either bisphosphatidic acid or a close analogue. These results suggest a new pathway for the turnover of phosphatidyl glycerol in E. coli.