Species pattern of phosphatidic acid, diacylglycerol, CDP-diacylglycerol and phosphatidylglycerol synthesized de novo in rat liver mitochondria

Rat liver mitochondria were incubated with [3H]glycerol 3-phosphate, ATP, CTP and coenzyme A allowing acylatin of glycerophosphate with endogenous fatty acids and the further conversion of labelled phosphatidic acid (PA) to diacylglycerol (DG), CDP-diacylglycerol (CDP-DG) and phosphatidylglycerol (PG). In these glycerolipids, the distribution of label among the individual molecular species was found to be similar, with 16:0-18:1, 16:0-18:2 and 18:0-18:2/16:0-16:0 being the main species. It was concluded that mitochondrial enzymes involved in the de novo synthesis of these glycerolipids exhibited no acyl selectivity for their substrates. The pattern of molecular species of mitochondrial PA, DG and CDP-DG closely approached that of the same glycerolipids synthesized de novo in isolated rat liver microsomes.

Liposomes as cyclosporin A carriers: positively charged lecithin-cholesterol liposomes associated with cyclosporin A do not inhibit biosynthesis of mitochondrial polyglycerophosphatides and microsomal phosphatidylinositol

Phosphatidylcholine (from egg yolk)-cholesterol-stearylamine (7:2:2.25, molar ratio) liposomes when associated with cyclosporin A (phosphatidylcholine:cyclosporin A = 2:0.07, molar ratio) do not inhibit significantly the biosynthesis of [3H]polyglycerophosphatides and [3H]phosphatidylinositol in mitochondrial and microsomal membranes, respectively, isolated from rat liver. These results are explained by possible protection of the liposomes by cyclosporin A against phospholipase A2 hydrolysis.

Synthesis of phosphatidylcholine and phosphatidylglycerol in rat lung mitochondria

The mitochondrial fraction of adult rat lung contains choline phosphotransferase (EC 2.7.8.2) activity which can not be explained by microsomal contamination estimated on the basis of marker enzyme distribution. Mitochondrial (14C)glycerol-3-phosphate incorporation into PC (phosphatidylcholine) can be distinguished from the microsomal incorporation by different sensitivity to N-ethylmaleimide inhibition. The data indicate that rat lung mitochondria have the intrinsic capability to synthesize PC. Both synthesis of PC and PG (phosphatidylglycerol) are susceptible to isotonic tryptic attack against the cytoplasmic face of isolated rat lung mitochondria, suggesting the outer membrane location of crucial activities involved in the formation of these phospholipids. Rat liver mitochondria are different from rat lung mitochondria with respect to their capability to synthesize PC, their rate of (14C)glycerol-3-phosphate incorporation into PG as well as the submitochondrial site of PG formation.

Modification of the biosynthesis and composition of polyglycerophosphatides in outer and inner mitochondrial membranes by cytidine liponucleotides

The biosynthesis of [3H]polyglycerophosphatides ([3H]phosphatidylglycerophosphate and [3H]phosphatidylglycerol) in mitochondrial and submitochondrial (outer and inner) membranes isolated from guinea pig liver was examined. Experimental results have established that the amount of biosynthesized [3H]polyglycerophosphatides and the relative amounts of biosynthesized [3H]phosphatidylglycerol and [3H]phosphatidylglycerolphosphate can be influenced by varying the composition of fatty acids in CDP-diglycerides and by altering the incubation time of the mixture containing CDP-diglycerides (obligatory precursor), sn-[2-3H]glycerol-3-phosphate and mitochondria or submitochondrial membranes. The changes thus obtained in respect to the amount and composition of biosynthesized [3H]polyglycerophosphatides are different in mitochondria and submitochondrial membranes. The highest amount of biosynthesized [3H]polyglycerophosphatides was obtained with CDP-didecanoin and inner mitochondrial membranes. The greatest accumulation of [3H]phosphatidylglycerol with CDP-didecanoin was obtained in mitochondria and outer mitochondrial membranes, while in inner mitochondrial membranes the amounts of [3H]phosphatidylglycerol and [3H]phosphatidylglycerolphosphate accumulated were approximately the same. In general, prolongation of the incubation time decreased the relative amounts of [3H]phosphatidylglycerolphosphate and increased the amount of accumulated [3H]phosphatidylglycerol, but the absolute amounts of these [3H]polyglycerophosphatides were more dependent on fatty acid composition of CDP-diglycerides tested. The following cytidine liponucleotides were tested: CDP-didecanoin, CDP-dipalmitin, CDP-diolein, and CDP-diglycerides containing saturated and unsaturated fatty acids similar to those in egg yolk lecithin. The formation of [3H]cardiolipin from [3H]phosphatidylglycerol in the presence of CDP-didecanoin and Mn2+ was found in both the outer and inner mitochondrial membranes.

Expression of the Saccharomyces cerevisiae PIS gene and synthesis of phosphatidylinositol in Escherichia coli

Expression of the Saccharomyces cerevisiae PIS gene encoding phosphatidylinositol synthase in Escherichia coli was achieved by inserting its coding sequence into lacZ on pUC8. The fused gene encoded a phosphatidylinositol synthase whose amino-terminal three amino acids had been replaced by the amino-terminal five amino acids of E. coli beta-galactosidase. E. coli cells bearing this recombinant plasmid produced a significant level of phosphatidylinositol synthase in the presence of a lacZ inducer, isopropylthio-beta-D-galactopyranoside. When the culture medium was supplemented with myo-inositol and isopropylthio-beta-D-galactopyranoside, the cells accumulated a substantial amount of phosphatidylinositol in their membranes. When a saturating level of myo-inositol was added, phosphatidylinositol constituted about 4% of the total phospholipids. Phosphatidylinositol accumulation occurred at the expense of phosphatidylglycerol. The ratio of phosphatidylethanolamine to total acidic phospholipids remained constant. The growth rate of phosphatidylinositol-containing E. coli cells did not differ significantly from that of cells with the normal phospholipid composition.

12-O-tetradecanoylphorbol-13-acetate activates phosphatidylethanol and phosphatidylglycerol synthesis by phospholipase D in cell lysates

A cell-free system for the synthesis of phosphatidylalcohols was developed in sonicates of HL-60 cells. With [32P]phosphatidylcholine as the exogenous substrate, both phosphatidylethanol and phosphatidylglycerol were formed through a phospholipase D-catalyzed transphosphatidylation of ethanol and glycerol, respectively. The transphosphatidylation by phospholipase D was stimulated in vitro by 12-O-tetradecanoylphorbol-13-acetate (TPA) and required the addition of ATP for an optimal response. GTP-gamma-S, an activator of G protein systems, also stimulated the process by an independent mechanism. It is postulated that the stimulation of phospholipid metabolism through phospholipase D activation represents an important mechanism whereby TPA might modulate intracellular signal generating systems or influence the activity of membrane-bound proteins by altering their lipid environment.

Species pattern of phosphatidylinositol from lung surfactant and a comparison of the species pattern of phosphatidylinositol and phosphatidylglycerol synthesized de novo in lung microsomal fractions

1. Phosphatidylinositol (PI) is a minor component of lung surfactant which may be able to replace the functionally important phosphatidylglycerol (PG) [Beppu, Clements & Goerke (1983) J. Appl. Physiol. 55, 496-502] without disturbing lung function. The dipalmitoyl species is one of the main species for both PI (14.4%) and PG (16.9%). Besides the C16:0--C16:0 species, the C16:0--C18:0, C16:0--C18:1, C16:0--C18:2 and C18:0--C18:1 species showed comparable proportions in the PG and PI fractions. These similarities of the species patterns and the acidic character of both phospholipids could explain why surfactant PG may be replaced by PI. 2. PI and PG were radiolabelled by incubation of microsomal fractions with [14C]glycerol 3-phosphate (Gro3P). For 11 out of 14 molecular species of PI and PG we measured comparable proportions of radioactivity. The radioactivity of these 11 species accounted together for more than 80% of the total. The addition of inositol to the incubation system decreased the incorporation in vitro of Gro3P into PG and CDP-DG (diacylglycerol) of lung microsomes (microsomal fractions), but did not change the distribution of radioactivity among the molecular species of PG. These results supported the idea that both acidic surfactant phospholipids may be synthesized de novo from a common CDP-DG pool in lung microsomes.

Production of a phosphatidylglycerol-like substance by genital flora bacteria

Bacteria contaminating amniotic fluid have anecdotally been shown to produce a phosphatidylglycerol-like substance, thus giving false positive tests for phosphatidylglycerol in vaginal pool fluid from patients with premature rupture of the membranes. Isolates of Escherichia coli, Proteus mirabilis, Acinetobacter calcoaceticus, Klebsiella pneumoniae, Staphylococcus aureus, coagulase-negative Staphylococcus, Streptococcus faecalis, and Streptococcus agalactiae (group B streptococcus) were grown in broth and analyzed for the presence of phosphatidylglycerol-like material by one-dimensional thin-layer chromatography and also by a polyclonal, immunologic slide agglutination test (Amniostat-FLM). All species demonstrated a positive test result for phosphatidylglycerol by either thin-layer chromatography, slide agglutination, or both. The material migrated separately from cardiolipin and phosphatidylethanolamine as determined by chromatography, but identically with the phosphatidylglycerol control. Gram-negative species were more strongly positive than gram-positive organisms. Colony counts on the order of 10(8) colony-forming units per milliliter were necessary to give positive test results for phosphatidylglycerol. The possible clinical implications of these findings are discussed.

Uptake of fatty acids by Mycoplasma capricolum

The energy requirements for fatty acid uptake by Mycoplasma capricolum were studied. Fatty acid transport and esterification to phospholipid appeared to be tightly coupled, since there was little intracellular accumulation of free fatty acid. Uptake was blocked by iodoacetate, n-ethylmaleimide, and p-chloromercuribenzoate. Glucose, glycerol, and potassium ions were necessary for fatty acid uptake by whole cells. A reduction in uptake was observed in cells treated with valinomycin or dicyclohexylcarbodiimide. The effect of temperature on the rate of oleate uptake showed a discontinuity at 24 degrees C. Above 24 degrees C an energy of activation of 4.6 kcal (ca. 19.2 kJ)/mol was obtained. The data suggest that uptake of fatty acid by M. capricolum is an energy-linked, protein-mediated process. A membrane-bound enzyme activity that catalyzed the synthesis of fatty acyl-hydroxamate was demonstrated. This activity was virtually independent or only marginally dependent on coenzyme A, depending on the assay system, but was stimulated approximately twofold by ATP.

Role of intracellular glycerol-3-phosphate in the synthesis of phosphatidylglycerol by freshly isolated adult rat alveolar type II cells

Synthesis of phosphatidylglycerol and phosphatidylinositol, phospholipid components of pulmonary surfactant, use the same precursor, CDP-diacylglycerol. In alveolar type II epithelial cells, extracellular myoinositol has been used to suppress phosphatidylglycerol synthesis, presumably by competing with glycerol-3-P for a common pool of CDP-diacylglycerol. We sought to see if extracellular lactate would increase acetate incorporation into phosphatidylglycerol by increasing glycerol-3-P. Lactate and 10 mM cytidine increased acetate incorporation into phosphatidylglycerol, whereas myoinositol and pyruvate decreased acetate incorporation into phosphatidylglycerol. Lactate increased the intracellular content of glycerol-3-P. We conclude that phosphatidylglycerol synthesis can, in part, be regulated by intracellular glycerol-3-P concentration, and we speculate that extracellular (alveolar) lactate may increase glycerol-3-P concentration in alveolar type II cells in vivo.

Comparison of cytidinediphospho-sn-1,2-diglyceride transfer from microsomal and liposomal to mitochondrial membranes

Transfer of [3H]CDP-diglycerides from isolated guinea pig liver microsomal and liposomal membranes to guinea pig mitochondrial membranes was studied by incubating microsomal or liposomal membranes carrying [3H]CDP-diglycerides with mitochondrial membranes and determining the CDP-diglyceride-dependent incorporation of sn-3-[14C]glycerolphosphate into mitochondrial [14C]polyglycerophosphatides. A significant difference in the amount of transferred [3H]CDP-diglycerides and the composition of mitochondrial [14C]polyglycerophosphatides was found depending on whether [3H]CDP-diglycerides were transferred from microsomal or liposomal membranes. This amount was around 12% when [3H]CDP-diglycerides were transferred from the microsomal membranes and around 4.6% when they were transferred from the liposomal membranes. Furthermore, about 60% of [14C]phosphatidylglycerol and 35% of [14C]phosphatidylglycerophosphate were found in the microsomes-mitochondria system and about 9% of [14C]phosphatidylglycerol and 79% of [14C]phosphatidylglycerophosphate were found in the liposomes-mitochondria system, establishing an important role for the membrane donor in the transfer of [3H]CDP-diglycerides to mitochondria. Furthermore, if the transfer of [3H]CDP-diglycerides from the microsomal to the mitochondrial membranes was assayed by the determination of [3H]CDP-diglycerides in reisolated mitochondrial membranes without further incorporation into mitochondrial polyglycerophosphates, it amounted to about 38%.

Culture of differentiated and undifferentiated type II cells from fetal rat lung

We have developed a relatively simple and reproducible method for the isolation and culture of both differentiated and undifferentiated type II cells from fetal rat lung. The technique involves an initial period of explant culture in serum and hormone free medium, followed by enzymatic dissociation of the explants, differential adhesion to remove fibroblasts, incubation of the cell pellet to promote aggregation of the type II cells and monolayer culture of the type II cells. The type II cells form clusters which are surrounded by scattered fibroblasts. When the technique was performed with three differential adhesion steps, cultures contained 86.0 +/- 1.4% type II cells. To obtain a higher degree of purity and greater yield, two differential adhesions followed by gentle trypsinization of the cultures which selectively removes the isolated fibroblasts was performed. This resulted in cultures with 89.4 +/- 1.7% type II cells. The differentiated fetal type II cell cultures were prepared from 19-day fetal rat lungs which were initially maintained in explant culture for 48 h. These differentiated cells demonstrated the characteristic morphologic features of type II cells including lamellar bodies and microvilli. Undifferentiated fetal cells were prepared in a similar manner from 18-day fetal rat lung maintained in explant culture for 24 h. These cells did not contain intracellular osmiophilic granules; the appearance of these granules could, however, be induced by hormones. For this reason they are considered to be pre-type II cells. The viability of the cultured cells was 97%. Both the differentiated and undifferentiated fetal type II cells specifically bound the Maclura pomifera lectin, a type II cell surface marker. The phospholipid profile of the fetal cells was similar to that of adult rat type II cells; the differentiated fetal cells, however, synthesized less phosphatidylcholine than the adult cells did, but more than the undifferentiated fetal cells. The differentiated fetal cells secreted phosphatidylcholine at a basal rate of 0.6% +/- 0.1% during a 90-min incubation. There was dose-dependent stimulation of phosphatidylcholine secretion after exposure to terbutaline. Maximum stimulation (76%) was observed at a concentration of 10 microM. This culture system provides a valuable model for studies of the maturation of the undifferentiated fetal type II cell and surfactant metabolism and secretion in the differentiated fetal type II cell.

Effect of chlorpromazine on the synthesis, hydrolysis, and transfer of microsomal cytidine liponucleotides and mitochondrial polyglycerophosphatides

The effect of chlorpromazine on subcellular biosynthesis, hydrolysis, and transfer of lipids and liponucleotides participating in the biosynthesis of polyglycerophosphatides in guinea pig liver was studied. Chlorpromazine showed an apparent stimulation of accumulation of phosphatidic acid and CDP-diglycerides in microsomal membranes and phosphatidylglycerolphosphate in mitochondrial membranes in a concentration-dependent manner that was influenced by incubation time and the nature of fatty acids in CDP-diglycerides. Transfer of membrane-bound CDP-diglycerides from microsomal to mitochondrial membranes was established by the CDP-diglyceride-dependent biosynthesis of phosphatidylglycerolphosphate and phosphatidylglycerol and appeared to be inhibited by the addition of chlorpromazine by about 20%. Evidence was obtained for the formation of a molecular complex between phosphatidic acid and chlorpromazine; this was thought to be responsible for the protection from phosphatidate phosphohydrolase at the concentrations of chlorpromazine and Mg2+ examined.

Selective use of palmitic acid over stearic acid for synthesis of phosphatidylcholine and phosphatidylglycerol in lung

The incorporation of [3H]palmitic acid and [14C]stearic acid into phospholipids in rabbit lung tissue was studied. Under equal molar concentrations of palmitate and stearate, palmitate was incorporated to the 1- and 2-positions of phosphatidylcholine (PC) and phosphatidylglycerol (PG) 2-3 times more than stearate. By contrast, palmitate was 30% less than stearate in phosphatidylethanolamine, phosphatidylinositol and phosphatidylserine. These results suggest that preferential utilization of palmitate over stearate, rather than substrate availability, determines the high content of palmitoyl at the 1- and 2-positions of PC and PG in lung.

Comparison of the enzyme activities of phosphatidylcholine, phosphatidylglycerol and phosphatidylinositol synthesis in freshly isolated type II pneumocytes and whole lung from the adult rat

We compared the activities of enzymes of phosphatidylcholine, phosphatidylglycerol and phosphatidylinositol synthesis in whole lung tissue and freshly isolated type II pneumocytes from adult rats. The activities of 1-acylglycerophosphocholine acyltransferase and CDPdiacylglycerol-glycerol-3-phosphate 3-phosphatidyltransferase were 2.9- and 4.4-fold higher, respectively, in type II cell sonicates than in whole lung homogenates. There was little difference between the type II cells and whole lung in the activities of choline kinase, choline-phosphate cytidyltransferase, cholinephosphotransferase, phosphatidate phosphatase, phosphatidate cytidylytransferase or CDPdiacylglycerol-inositol 3-phosphatidyltransferase. Since the type II cell is the source of pulmonary surfactant, and disaturated phosphatidylcholine and phosphatidylglycerol are major components of surfactant, it is of interest that this cell is enriched in the activities of enzymes exclusively involved in the synthesis of these lipids. In view of possible proteolytic damage during isolation we compared freshly isolated type II cells with those cultured for 1 day. The rates of incorporation of [methyl-3H]choline and [2-3H]glycerol into phospholipids, L-[U-14C]phenylalanine into protein and [methyl-3H]thymidine into DNA were the same in the freshly isolated and cultured cells. The composition of the phospholipids synthesized from [2-3H]glycerol and sodium [1-14C]acetate were also the same. The freshly isolated cells were at least 90% pure and did not release significant amounts of lactate dehydrogenase. Since use of freshly isolated cells avoids cell loss during culture they provide an attractive alternative, particularly in studies requiring large amounts of material.

Participation of the microsomal CDP-diglycerides in the mitochondrial biosynthesis of phosphatidylglycerol

Participation of microsomal CDP-diglycerides in mitochondrial biosynthesis of phosphatidylglycerol was studied by [3H]palmitoyl, [14C]linoleoyl, and [14C]arachidonoyl CDP-diglycerides and [3H]CDP-diglycerides which were bound to microsomal membranes, incubated with unlabelled mitochondrial membranes, and further incubated in the presence of radioactive sn-glycero-3-phosphate under conditions required for mitochondrial phosphatidylglycerol biosynthesis. Ten to 15% of microsomal radioactive CDP-diglycerides was transferred to mitochondrial membranes and incorporated into mitochondrial radioactive lipids identified as phosphatidylglycerol, phosphatidylglycerophosphate, and, when [14C]linoleoyl CDP-diglycerides were used, diphosphatidylglycerol (cardiolipin).

Perinatal development of myoinositol uptake into lung cells: surfactant phosphatidylglycerol and phosphatidylinositol synthesis in the rabbit

It has been proposed that the high serum myoinositol promotes fetal growth and affects development of lung surfactant. However, it is unclear how the extracellular myoinositol becomes available in specific cells and whether there are developmental differences in myoinositol uptake. In the present study the mechanisms and perinatal development of intracellular myoinositol uptake into rabbit lung cells were investigated. Lung slices, lung explants, and type II alveolar cells were used. Evidence of saturable, sodium- and energy-dependent, and of non-saturable, sodium- and energy-independent myoinositol uptake was found. The nonsaturable uptake decreased by 67% during spontaneous maturation, as studied in lung slices. Beta-methasone (0.2 mg/kg days 26.3 and 27.3, to the doe) decreased by 65% the nonsaturable myoinositol uptake in 28-day-old fetuses. However, the saturable uptake revealed only small changes during perinatal development. The effect of extracellular myoinositol on surfactant phospholipid synthesis was evaluated in lung explants from 28-day-old fetuses, cultured for 2 days. In the presence of 10(-6) M dexamethasone the concentration of extracellular myoinositol, required for half-maximal inhibition of surfactant phosphatidylglycerol incorporation was higher than in explants grown without the hormone (approximately 0.4 versus 0.2 mM). However, in the microsomal fraction the phosphatidylglycerol incorporation was always inhibited by as low as 4 microM myoinositol. Myoinositol was taken up by isolated type II cells preferably by nonsaturable mechanism. The phosphatidylglycerol incorporation was less sensitive to extracellular myoinositol in adult than in fetal cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of myo-inositol in impairment of fetal lung phosphatidylglycerol biosynthesis in the diabetic pregnancy: physiological consequences of a phosphatidylglycerol-deficient surfactant in the newborn rat

To test the hypothesis that the deficit of fetal lung surfactant phosphatidylglycerol (PG) in diabetic pregnancies was due to increased plasma myo-inositol, lung PG content and plasma myo-inositol level were compared in fetuses of streptozotocin-diabetic rats and in fetuses of rats injected with myo-inositol during the 4 last gestational days. An inverse linear correlation was established between circulating myo-inositol and lung phosphatidylglycerol content, including data from fetuses of diabetic rats, which is consistent with the hypothesis. Changes in phospholipid synthetic rates were estimated in fetuses of rats given myo-inositol by measuring incorporation of labelled glycerol on a six hour period on the 21st gestational day, after i.v. injection to the mother. Incorporation into PG was 2.5 times smaller but incorporation into PI or PC were not modified. Pulmonary function in PG-deficient newborns of rats given a high-dosage myo-inositol was assessed by pressure/volume measurements on the lung in situ and by measurement of oxygen tension in aortic blood. Opening pressure of alveoli for lung inflation was increased and blood oxygenation was reduced (30%) in newborns with PG-deficient surfactant as compared with controls, thus suggesting an important physiological role for surfactant PG at birth.

Cytidine monophosphate-dependent synthesis of phosphatidylglycerol in permeabilized type II pneumonocytes

Results of previous investigations support the proposition that, in type II pneumonocytes, CMP is involved in integration of the synthesis of phosphatidylcholine and phosphatidylglycerol for lung surfactant. In the present investigation, the amount of CMP in rat type II pneumonocytes was altered directly and resultant changes in the synthesis of phosphatidylglycerol were examined. Type II pneumonocytes were made permeable to CMP by treatment with Ca2+-free medium, and phosphatidylglycerol synthesis was then assessed by measurement of the incorporation of a radiolabelled precursor, [14C]glycerol 3-phosphate, that was not effectively utilized by cells that resisted permeabilization. Incorporation of [14C]glycerol 3-phosphate into phosphatidylglycerol (but not into other lipids) was stimulated greatly by CMP (half-maximal stimulation at approx. 0.1 mM). CMP stimulated the incorporation of [14C]glycerol 3-phosphate into both the phosphatidyl moiety and the head group of phosphatidylglycerol. Incorporation of [14C]palmitate into phosphatidylglycerol was also stimulated by CMP. myo-Inositol, at concentrations found in foetal-rat serum (0.2-2.0 mM), inhibited CMP-dependent incorporation of [14C]glycerol 3-phosphate into phosphatidylglycerol and promoted, instead, CMP-dependent incorporation into phosphatidylinositol. These data, when extrapolated to foetal type II pneumonocytes, are consistent with the view that the developmental increase in the synthesis of phosphatidylglycerol for surfactant by foetal lungs is promoted by the increase in intracellular CMP and the declining availability of myo-inositol that were found previously to be associated with this period of development.

Genetic manipulation of membrane phospholipid composition in Escherichia coli: pgsA mutants defective in phosphatidylglycerol synthesis

Unique mutants of Escherichia coli K-12, defective in phosphatidylglycerol synthesis, have been isolated from a temperature-sensitive strain incubated at its nonpermissive temperature. The parent strain had excess phosphatidylglycerol by harboring both the pss-1 allele [coding for a temperature-sensitive phosphatidylserine synthase (EC 2.7.8.8)] and the cls- allele (responsible for a defective cardiolipin synthase). The newly acquired mutations caused better growth at higher temperatures. One of the mutations (pgsA3) has been identified in the structural gene for phosphatidylglycerophosphate synthase [glycerophosphate phosphatidyltransferase (EC 2.7.8.5)]. Phospholipid compositions of these mutants were remarkable; phosphatidylethanolamine was the sole major lipid. In media with low osmotic pressures, these cells grew more slowly than the wild-type cells. They grew normally without recovering from the phospholipid abnormality in media appropriately supplemented with sucrose and MgCl2. Formation of cardiolipin and phosphoglycerol derivatives of membrane-derived oligosaccharides was reduced in a pgsA3 mutant. E. coli strains having the pgsA3, pss-1, and cls- mutations, either individually or in combination, constitute an empirical system in which the molar ratio of three major membrane phospholipids can be variously altered.

Effect of liposomes on substrate uptake by isolated guinea-pig liver mitochondrial and microsomal membranes

The effect of adding small unilamellar lecithin liposomes, prepared in the presence of cytidine-diphosphoryl-1,2-diglycerides (CDP-diglycerides) or cytochrome c, on microsomal biosynthesis of phosphatidylinositol and NADPH-cytochrome c reduction and on mitochondrial biosynthesis of polyglycerophosphatides and succinate-cytochrome c reduction was studied in isolated guinea-pig liver subcellular membranes. Both microsomal biosynthesis of phosphatidylinositol and mitochondrial biosynthesis of phosphatidylglycerol were significantly reduced when CDP-diglycerides associated with liposomes were used, suggesting that some CDP-diglycerides were entrapped by liposomal membranes and were not available to subcellular membranes as substrates. The degree of decrease in phospholipid biosynthesis depended on the membrane and the nature of fatty acids in CDP-diglycerides. The composition of mitochondrial polyglycerophosphatides synthesized in the presence of CDP-diglycerides-liposomes was also affected in respect to the amount of phosphatidylglycerol formed. The reduction of cytochrome c in both microsomal and mitochondrial membranes was also decreased when liposomes were present in the assay system, but to a lesser degree than the phospholipid biosynthesis. These results indicate that the cytochrome c liposome association did not provide efficient protection of this substrate from the subcellular reduction. When chlorpromazine was also present with liposomes in the assay system, the NADPH-cytochrome c reduction in microsomes was scarcely affected, while the succinate-cytochrome c reduction in mitochondria was dependent on the concentration of chlorpromazine and could be completely abolished. These results were interpreted in terms of liposomal interaction with substrates in competition with subcellular membranes for the same substrates.