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At least 19 recordsLinked to original sources
PubMed1979

Kinetics of the in vivo labeling of the acyl groups of rabbit lung phosphatidylcholine and disaturated phosphatidylcholine.

The kinetics of labeling of lung phosphatidylcholine and disaturated phosphatidylcholine were studied for periods from 0.75--120 min following intravenous injection of radiolabeled palmitic acid and choline into 3-day-old rabbits. The labeled palmitic acid was cleared rapidly from plasma, and rapidly appeared with identical incorporation kinetics in both phosphatidylcholine and disaturated phosphatidylcholine. The 2-acyl positions of both phosphatidylcholine and disaturated phosphatidylcholine were labeled preferentially soon after [14C]palmitic acid injection. The specific activities of palmitic acid in the 2-acyl positions of phosphatidylcholine and disaturated phosphatidylcholine 0.75 min after injection of labeled palmitic acid were 3.4 and 1.9 times, respectively, the specific activities of palmitic acid in the 1-acyl positions. By 120 min the label had randomized between the 1-acyl and 2-acyl positions, and the kinetics of that randomization were defined for both phosphatidylcholine and disaturated phosphatidylcholine. Choline did not pulse label lung phosphatidylcholine or disaturated phosphatidylcholine. The choline label appeared with equal specific activities in both phosphatidylcholine and disaturated phosphatidylcholine. Thus no analysis of the de novo synthesized product via the CDP-choline pathway was possible.

Acylation↗
PubMed1979

Determination of the hydrophobic binding site of phosphatidylcholine exchange protein with photosensitive phosphatidylcholine.

1-Acyl-2-(7-(4-azido-2-nitrophenoxy)-[1-14C]heptanoly)-sn-glycero-3-phosphocholine was synthesized in order to study the lipid-binding site of the phosphatidylcholine exchange protein from bovine liver. Photosensitive phosphatidylcholine was incorporated into the protein by incubation with vesicles of this phosphatidylcholine derivative. The lipid-protein complex was separated from the vesicles by chromatography on Biogel A-0.5m. Photolysis of the complex by irradiation with light of a high pressure mercury lamp at a wavelength above 340 nm generated the highly reactive nitrene. Sodium dodecyl sulfate gel electrophoresis of the photolysed complex indicated that 30% of the endogenous 14C-labeled phosphatidylcholine was covalently linked to the protein. Peptides were isolated after digestion of the photolysed complex with protease from Staphylococcus aureus and trypsin. It was determined that the 2-acyl chain of the phosphatidylcholine molecule was linked to the peptide segment -Gly-Ser-Lys-Val-Phe-Met-Tyr-Tyr-. This segment was part of a protease peptide of about 65 residues of which the sequence was determined by Edman degradation for the first 38 residues. This peptide contains a cluster of apolar residues -Val-Phe-Met-Tyr-Tyr-Phe with an extremely high hydrophobicity index and with a predicted beta-sheet conformation. It is concluded that this hydrophobic cluster forms part of the binding site.

Amino Acid Sequence↗
PubMed1979

Inside-outside distribution and diffusion of phosphatidylcholine in rat sarcoplasmic reticulum as determined by 13C NMR and phosphatidylcholine exchange protein.

1. The transverse distribution of phosphatidylcholine in rat sarcoplasmic reticulum was investigated employing 13C NMR in conjunction with the shift reagent DyCl3. 2. Sarcoplasmic reticulum phosphatidylcholine was enriched with 13C by feeding rats a diet containing [N-Me3-13C]choline. Up to 32% of the sarcoplasmic reticulum phosphatidyl-[N-Me3-12C]choline was replaced by phosphatidyl-[N-Me3-13C]choline. 3. Titration of 13C-enriched sarcoplasmic reticulum with Dy3+ indicates that 40% of the phosphatidyl-[N-Me3-13C]choline is exposed to the external medium, whereas 60% is shielded from interaction with Dy3+. 4. Incubation of 32P-labelled sarcoplasmic reticulum with excess mitochondria and phosphatidylcholine exchange protein results in a fast transport of approx. 80% of [32P]phosphatydylcholine to the mitochondria indicating that part of the phosphatidylcholine pool is involved in a rapid transbilayer movement.

Animals↗
PubMedDate not supplied

The solubilisation of some steroids by phosphatidylcholine and phosphatidylcholine-cholesterol vesicles.

The solubility of the three steroid hormones, progesterone, testosterone, and estradiol-17 beta in water and phosphatidylcholine vesicles was measured after shaking and ultrasonication. All three steroids have low water solubility, which increases considerably at sonication for testosterone and estradiol-17 beta. The phosphatidylcholine vesicles have a very small solubilising capacity for the steroids; about 20 mumol/mol. This increases at sonication for estradiol-17 beta and decreases for testosterone. The capacity for progesterone is almost unaltered. The incorporation of cholesterol in the vesicles decreased the solubilisation capacity for testosterone and estradiol-17 beta but increased that for progesterone of shaked preparations. For the sonicated systems the cholesterol decreased the solubilising capacity for estradiol-17 beta but increased that for testosterone. The solubilisation experiments indicate that the steroid hormones are solubilised in the hydrocarbon part of the phosphatidylcholine bilayer and also 13CNMR results support this conclusion.

Cholesterol↗
PubMed1978

The synthesis of phosphatidylcholine by adult rat lung alveolar type II epithelial cells in primary culture.

1. The formation of phosphatidylcholine from radioactive precursors was studied in adult rat lung alveolar type II epithelial cells in primary culture. 2. The incorporation of [Me-14C]choline into total lipids and phosphatidylcholine was stimulated by addition of palmitate, whereas the incorporation of [U-14C]glucose into phosphatidylcholine and disaturated phosphatidylcholine was stimulated by addition of choline. Addition of glucose decreased the absolute rate of incorporation of [1(3)-3H]glycerol into total lipids, phosphatidylcholine and disaturated phosphatidylcholine, decreased the percentage [1(3)-3H]glycerol recovered in phosphatidylcholine, but increased the percentage phosphatidylcholine label in the disaturated species. 3. At saturating substrate concentrations, the percentages of phosphatidylcholine radioactivity found in disaturated phosphatidylcholine after incubation with [1-(14)C]acetate (in the presence of glucose) [1-(14)C]palmitate (in the presence of glucose), [Me-14C]choline (in the presence of glucose and palmitate) and [U-14C]glucose (in the presence of choline and palmitate) were 78, 75, 74 and 90%, respectively. 4. Fatty acids stimulated the incorporation of [U-14C]glucose into the glycerol moiety of phosphatidylcholine. The degree of unsaturation of the added fatty acids was reflected in the distribution of [U-14C]glucose label among the different molecular species of phosphatidylcholine. It is suggested that the glucose concentration in the blood as related to the amount of available fatty acids and their degree of unsaturation may be factors governing the synthesis of surfactant lipids.

Acetates↗
PubMed1979

Quantitation of phosphatidylcholine secretion in lung slices and primary cultures of rat lung cells.

Rat lung slices and isolated rat lung cells were used to study the secretion of phosphatidylcholine by the lung in vitro. The rate of incorporation of [(3)H]choline by lung slices was 20-fold greater than by liver slices and 4-fold greater in lung cells compared to confluent skin fibroblasts. Labeling lung slices or cells with [(3)H]choline for up to 8 hr failed to reveal a significant amount of labeled phosphatidylcholine in the medium of either system compared to the medium from liver slice or fibroblast controls. Labeling of isolated lung cells for up to 24 hr, with or without 10% fetal calf serum, also showed no significant difference in the amount of labeled phosphatidylcholine in the medium compared to control fibroblast cultures. Washing labeled lung slices or cells with a nonlysing concentration of Triton X-100 (0.05%) did not selectively release labeled phosphatidylcholine, indicating that any secreted phosphatidylcholine did not adhere to the surface of the lung slices or cells. Experiments were performed to determine whether the small amount of phosphatidylcholine in the medium and detergent-released phosphatidylcholine was similar to the tissue and cell phosphatidylcholine. The saturated fatty acid composition of the phosphatidylcholine released by Triton X-100 and in the medium (from lung slices) was identical to that of the tissue phosphatidylcholine. In addition, the relative labeling rates of the phospholipids released by Triton X-100 and in the medium (labeled with [(14)C]glycerol) were identical to those of the tissue and cell phospholipids. Based on these results, we conclude that phosphatidylcholine is not secreted by lung slices and lung cells in large amounts compared to controls. The implication of these data is that pulmonary surfactant material may actually not be secreted by the lung in vitro, and perhaps in vivo, in the manner that is currently generally accepted.

Animals↗
PubMed1979

Effect of alcohols on the collagen-phosphatidylcholine interaction.

The interaction of phosphatidylcholine dispersions with acid soluble collagen separated from the skin of one month-old swine was studied to define the conditions facilitating the association of the collagen with lipids. When acid soluble collagen and phosphatidylcholine dispersions were incubated in 75 mM citrate buffer of pH 3.7 at 25 degrees C, the reisolated collagen fibrils did not contain appreciable amounts of phosphatidylcholine. However, the presence of n-propanol greatly promoted the retention of phosphatidylcholine, the amount of phosphatidylcholine associated being nearly 30% of collagen on a weight basis under optimal conditions. In contrast, methanol, ethanol, isopropanol, and n-butanol did not appreciably enhance the association of phosphatidylcholine with collagen. A limited inhibition of phosphatidylcholine retention was observed upon addition of sodium chloride to the propanol medium. The interaction of phosphatidylcholine with acid soluble collagen decreased sharply when temperature was increased above 30 degrees C; almost no phosphatidylcholine-collagen association occured at 40 degrees C. It appears that the enhanced association in the presence of n-propanol is due to a looseing of the collagen triple helix that exposes hydrophobic sites necessary for the interaction. However, the conversion of the triple helical structure to the random coil conformation by heating prevents the association of phosphatidylcholine with acid soluble collagen.

Alcohols↗
PubMed1979

The labeling of lung phosphatidylcholine in premature rabbits.

Lung phosphatidylcholine metabolism was studied in vivo in premature rabbits delivered by cesarean section as early in gestation as compatible with prolonged viability (28.9 days). The newborn rabbits initially required supplemental oxygen and had respiratory distress. The amount of phosphatidylcholine isolated from the lung parenchyma changed little over the first 3 days of life, while phosphatidylcholine in the alveolar wash increased in 3 days from 0.05--3.1 mumol/50 g animal. The phosphatidylcholine of the lungs of the premature rabbits was pulse labeled with isotopically labeled palmitic acid, choline, and phosphate given to the pregnant does 10 min before delivery of the newborns. After the initial incorporation period, the total amount of radioactive precursor palmitic acid, choline, or 32P) incorporated into lung phosphatidylcholine did not change for a period of 4 days. Labeled phosphatidylcholine was detected initially in alveolar wash 3 hr after administration of the three precursors and continued to accumulate for many hours. The biological half-life values for lung and alveolar phosphatidylcholine indicated that phosphatidylcholine was turning over very slowly. However, if the effect of dilution on the measured specific activity caused by phosphatidylcholine accumulation was considered, virtually no labeled alveolar or lung phosphatidylcholine disappeared during the 3--4 days of these observations. These results with premature newborn rabbits were similar to those for term newborn rabbits, but different from similar measurements made in the adult rabbit.

Age Factors↗
PubMed1979

Regulation of phosphatidylcholine metabolism by cyclic AMP in a model alveolar type 2 cell line.

The influence of cyclic AMP on the metabolism of phosphatidylcholine, the major component of pulmonary surfactant was examined in a cell line (A549) with type 2 pneumonocyte characteristics. It was found that cyclic AMP increased both the total amount of phosphatidylcholine and disaturated phosphatidylcholine as well as the incorporation of [3H]choline into these fractions. The effect was specific for cyclic AMP since 5'-AMP, adenosine, and cyclic GMP did not alter phosphatidylcholine or disaturated phosphatidylcholine levels. Cyclic AMP had no effect on phosphatidylcholine and disaturated phosphatidylcholine metabolism in another non-type 2 human epithelial cell line (MA-160). Since the ability of various cyclic AMP analogs to increase phosphatidylcholine and disaturated phosphatidylcholine levels was correlated with their ability to activate protein kinase, it seems likely that a protein phosphorylation mechanism is involved in controlling phosphatidylcholine metabolism.

Animals↗
PubMed1979

Use of liposomes in probing the uptake of liposomal phosphatidylcholine by rabbit lung in vitro.

The purpose of this study was to characterize the uptake of liposomal phosphatidylcholine by lung tissue and its subcellular organelles. Multilamellar liposomes were prepared from egg yolk phosphatidylcholine, dicetyl phosphate, and cholesterol (molar ratio 7 : 2 : 1). Liposomal phosphatidylcholine labeled with [1-14C]dipalmitoyl phosphatidylcholine was taken up by lung slices and incorporated into subcellular organelles including lamellar bodies, mitochondria, and microsomes. In addition, when liposomes were incubated with lamellar bodies, mitochondria, or microsomes, the transfer of liposomal phosphatidylcholine to these subcellular fractions was facilitated by the cytosolic fraction. In tissue slice experiments after 1 h of incubation, about 86% of the total radioactivity absorbed by lung slices and subcellular organelles was recovered in phosphatidylcholine. The ratio of the radioactivity of fatty acids at 1- and 2-positions of dipalmitoyl phosphatidylcholine recovered from all fractions was nearly 1 : 1. This suggests that most phosphatidylcholine molecules were taken up intact. In conclusion, this study provides a method using liposomes as a tool for probing the phosphatidylcholine transfer mechanism in lung.

Animals↗
PubMed1979

[High phosphatidylcholine weights compared to lysophosphatidylcholine weights, in micellar intestinal contents, in the rat (author's transl)].

Casein hydrolysat, lactose and lipids (100 mg of fatty acids) were introduced in the stomach of rats by a gastric tube: either pure tri-oleoylglycerol, or phospholipids, or phosphatidylcholines, or the mixture 9/1 to fatty acid weight of tri-oleoylglycerol-phospholipids or phosphatidylcholines. The rats were killed 2 h later. The intraluminal intestinal lipids of the oil and micellar phases were separated after microfiltration (Millipore filters) in preference to the filtration by gel chromatography on polyacrylamide agarose, as an hydrolysis of intraluminal phospholipid occurred after the column elution. 1. After a quantitative recovery of the intestinal lipids (no separation of the oil and micellar phases), a strong hydrolysis of the tri-oleoyglycerol was observed; in opposition, large amounts of intact phospholipids appeared. 2. After isolation of the micellar phases, no triglycerides were recovered, but fatty acids and partial glycerides from the hydrolysed tri-oleoylglycerol and dietary phosphatidylcholines and small quantities of lyso-phosphatidylcholines (hydrolysed forms) were present. 3. After ingestion of the tri-oleoylglycerol as lipid dietary source, the intestinal micellar phases contained endogenous phosphatidylcholines and a few amounts of lysophosphatidylcholines, which had mainly bile origin, since the fatty acid composition of these micellar phosphatidylcholines approached the bile phosphatidylcholine fatty acid composition. The micellar lysophosphatidylcholine masses represented one-fourth of the micellar phosphatidylcholine masses. 4. In these experiments the phosphatidylcholine lysophosphatidylcholine ratio was always high: this means that small quantities of exogenous and endogenous lysophosphatidylcholines appeared in the micellar phases.

Animals↗
PubMed1976

Study of the transverse diffusion of spin-labeled phospholipids in biological membranes. II. Inner mitochondrial membrane of rat liver: use of phosphatidylcholine exchange protein.

Spin-labeled phosphatidylcholine was incorporated into the membrane of isolated "inner membrane+matrix" particles of rat liver mitochondria by incubation with sonicated spin-labeled phosphatidylcholine vesicles at 22 degrees C. When the spin label was on the acyl chain the incorporation of phosphatidylcholine into the membrane was stimulated by the presence of the phosphatidylcholine exchange protein extracted from rat or beef liver. On the other hand no stimulation was observed when the nitroxide was on the polar head-group. When spin-labeled phosphatidycholine was incorporated into the mitochondrial membrane in the absence of phosphatidylcholine exchange protein, ascorbate treatment at 0 degrees C reduced the EPR signal of the spin-labeled membranes by approximately 50%, indicating that fusion incorporates molecules equally on both sides of the membrane. On the other hand when spin-labeled phosphatidylcholine was incorporated in the presence of the exchange protein most of the EPR signal could be destroyed by the ascorbate treatment at 0 degrees C, indicating that the spin-labeled phosphatidylcholine had been selectively incorporated in the outer layer of the membrane. Finally when the label is on the polar head-group the inner content of mitochondria reduces the label facing the matrix, thus creating again an anisotropy of the labeling. The anisotropic distribution of spin-labeled phosphatidylcholine in the mitochondrial membrane was found to be stable at 25 degrees C for more than 2 h. It is therefore concluded that the rate of outside-inside and inside-outside transitions are extremely slow (half-life greater than 24 h).

Animals↗
PubMed1979

The involvement of the lipid phase transition in the plasma-induced dissolution of multilamellar phosphatidylcholine vesicles.

Unsonicated liposomes prepared from dimyristoyl phosphatidylcholine were nearly completely dissolved during a 3 h incubation with rat plasma at or close to the phase-transition temperature of 24 degrees C. At 37 or 15 degrees C virtually no liposomal disintegration was observed even after 24 h of incubation. The liposomal solubilization, which was monitored by turbidity measurements or by determination of phospholipid sedimentability, was accompanied by the formation of a phospholipid-protein complex similar or identical to the one we previously reported to be formed from sonicated liposomes of egg phosphatidylcholine (Scherphof, G., Roerdink, F., Waite, M. and Parks, J. (1978) Biochim. Biophys. Acta 542, 296--307). Unsonicated multilamellar liposomes made of egg phosphatidylcholine were completely resistant to the dissolving potency of plasma when incubated at 37 degrees C. Liposomes from equimolar mixtures of dimyristoyl and dipalmitoyl phosphatidylcholine were only degraded by plasma in the temperature range between 30 and 35 degrees C at which temperature this cocrystallizing phospholipid mixture undergoes a phase transition. However, even at these temperatures the rate of dissolution of this mixture was significantly lower than of dimyristoyl phosphatidylcholine at 24 degrees C. In the dissolving process of this mixture a slight preference for the lower-melting component was observed. The ability of cholesterol to completely abolish the susceptibility of dimyristoyl phosphatidylcholine liposomes to plasma at a 1:2 molar ratio of cholesterol to phospholipid substantiates the essential role of the phase transition in the process of liposome solubilization. When liposomes of the monotectic mixtures dimyristoyl and distearoyl phosphatidylcholine or dilauroyl and distearoyl phosphatidylcholine were incubated with plasma at temperatures in between those at which the constituent lipids undergo a phase change in the mixture, the liposomes were slowly dissolved. Under those conditions a selective removal of the lipids in the liquid-crystalline phase was observed. It is concluded that for the plasma-induced dissolution of unsonicated liposomes, which is most probably achieved by interaction with (apo)lipoproteins, the presence of phase boundaries is required in much the same way as was first reported for phospholipases by Op den Kamp, J.A.F., de Gier, J. and Van Deenen, L.L.M. (1974) Biochim. Biophys. Acta 345, 253--256).

Animals↗
PubMed1979

Evidence for an oleoyl phosphatidylcholine desaturase in microsomal preparations from cotyledons of safflower (Carthamus tinctorius) seed.

1. [14C]Oleoyl-CoA was metabolized rapidly and essentially completely by microsomal preparations from developing safflower (Carthamus tinctorius) cotyledons, and most of the [14C]oleate was incorporated into 3-sn-phosphatidylcholine. 2. In aerobic reaction mixtures containing NADH2 the [14C]oleate in 3-sn-phosphatidylcholine was converted into [14C]linoleate without any change in the specific radioactivity of the lipid. Over a 60 min incubation period the extent of conversion of [14C]oleoyl phosphatidylcholine into [14C]linoleoyl phosphatidylcholine was generally greater than 60%. The rate of desaturation of endogenous [14C]oleoyl phosphatidylcholine labelled from [14C]oleoyl-CoA was much greater that of exogenous [14C]dioleoyl phosphatidylcholine the specific radioactivity of the oleoyl moiety of the lipid remained constant, indicating that labelled and unlabelled oleate were desaturated at the same rate. On this assumption an initial rate of desaturation of about 15 nmol of oleate desaturated/min per mumol of 3-sn-phosphatidylcholine was estimated. 4. [14C]Oleate esterified at positions 1 and 2 of both endogenous and exogenous 3-sn-phosphatidylcholine was desaturated. 5. Attempts to demonstrate the presence of an oleoyl-CoA desaturase in safflower microsomal fractions by the appearance of linoleoyl-CoA in reaction mixtures were inconclusive.

Acyl Coenzyme A↗
PubMed1977

Induction of a relatively fast transbilayer movement of phosphatidylcholine in vesicles. A 13CNMR study.

[N-13CH3]Phosphatidylcholines are introduced into the outer monolayer of phosphatidylcholine vesicles with the phosphatidylcholine exchange protein from bovine liver. The transbilayer distribution of the [N-13CH3]phosphatidyl-choline is measured with 13C NMR. The transbilayer movements of [N-13CH3]-dioleoyl phosphatidylcholine and [N-13CH3]dimyristoyl phosphatidylcholine at 30 degrees C in vesicles composed of these phosphatidylcholines are extremely slow processes with estimated half-times of days. [N-13CH3]Dioleoyl phosphatidyl-choline introduced into dimyristoyl phosphatidylcholine vesicles migrates from the outer to the inner monolayer with a half-time of less than 12 h. The data suggest that differential changes in the lateral packing of the two monolayers might be a driving force for transbilayer transport of phospholipids.

Animals↗
PubMed1977

The effect of phosphatidylcholine to sphingomyelin mole ratio on the dynamic properties of sheep erythrocyte membrane.

Sheep red blood cells are shown to incorporate phosphatidylchline when incubated in human plasma in the presence of EGTA. This treatment results in up to a 5-fold increase in mol ratio of phosphatidylcholine to sphingomyelin. By replacing EGTA with Ca+ the increase of phsphatidylcholine content is completely inhibited, due to the activation of the membrane bound lecithinase which rapidly degrades the incorporated phosphatidylcholine. Analogous treatments of the isolate membranes resulted in similar phosphatidylcholine incorporation but in the presence of Ca+ a residual phosphatidylcholine uptake was still oberved. These results suggest that in the isolated membranes small amounts of phosphatidylcholine can be incorporated into an additional region which is unavailable for the membrane lecithinase. The increase in the phosphatidylcholine to sphingomyelin mol ratio in sheep red blood cells is concomitant with an increase in lipid fluidity, as well as increase in osmotic fragility9

Animals↗
PubMed1979

Exchange of phospholipids between unilamellar vesicles of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine and plasma very low density lipoproteins.

Purified phosphatidylcholine exchange protein from bovine liver was used to exchange [14C]dipalmitoyl phosphatidylcholine from sonicated vesicles to human plasma very low density lipoproteins (VLDL). The exchange of [14C]-dipalmitoyl phosphatidylcholine for VLDL phospholipids was temperature dependent and linear with respect to time and amount of exchange protein. In the absence of the exchange protein, less than 10% of the [14C]dipalmitoyl phosphatidylcholine was transferred. At an initial weight ratio of [14C]-dipalmitoyl phosphatidylcholine vesicles to VLDL phospholipid (1.2 mg) of 2.2, the exchange protein (14 microgram) replaced 55% of the VLDL phospholipids with [14C]dipalmitoyl phosphatidylcholine in 15 min; VLDL protein and cholesterol content were unaltered. From these studies we conclude that the exchange protein is a useful method to alter the phospholipid composition of VLDL under conditions such that there is minimal perturbation of the lipoprotein.

Androgen-Binding Protein↗