Role of carnitine and carnitine palmitoyltransferase as integral components of the pathway for membrane phospholipid fatty acid turnover in intact human erythrocytes.

The deacylation and reacylation process of phospholipids is the major pathway of turnover and repair in erythrocyte membranes. In this paper, we have investigated the role of carnitine palmitoyltransferase in erythrocyte membrane phospholipid fatty acid turnover. The role of acyl-L-carnitine as a reservoir of activated acyl groups, the buffer function of carnitine, and the importance of the acyl-CoA/free CoA ratio in the reacylation process of erythrocyte membrane phospholipids have also been addressed. In intact erythrocytes, the incorporation of [1-14C]palmitic acid into acyl-L-carnitine, phosphatidylcholine, and phosphatidylethanolamine was linear with time for at least 3 h. The greatest proportion of the radioactivity was found in acyl-L-carnitine. Competition experiments using [1-14C]palmitic and [9,10-3H]oleic acid demonstrated that [9,10-3H]oleic acid was incorporated preferentially into the phospholipids and less into acyl-L-carnitine. When an erythrocyte suspension was incubated with [1-14C]palmitoyl-L-carnitine, radiolabeled palmitate was recovered in the phospholipid fraction, and the carnitine palmitoyltransferase inhibitor, 2-tetradecylglycidic acid, completely abolished the incorporation. ATP depletion decreased incorporation of [1-14C]palmitic and/or [9,10-3H]oleic acid into acyl-L-carnitine, but the incorporation into phosphatidylcholine and phosphatidylethanolamine was unaffected. In contrast, ATP depletion enhanced the incorporation into phosphatidylcholine and phosphatidylethanolamine of the radiolabeled fatty acid from [1-14C]palmitoyl-L-carnitine. These data are suggestive of the existence of an acyl-L-carnitine pool, in equilibrium with the acyl-CoA pool, which serves as a reservoir of activated acyl groups. The carnitine palmitoyltransferase inhibition by 2-tetradecylglycidic acid or palmitoyl-D-carnitine caused a significant reduction of radiolabeled fatty acid incorporation into membrane phospholipids, only when intact erythrocytes were incubated with [9,10-3H]oleic acid. These latter data may be explained by the differences in rates and substrates specificities between acyl-CoA synthetase and the reacylating enzymes for palmitate and oleate, which support the importance of carnitine palmitoyltransferase in modulating the optimal acyl-CoA/free CoA ratio for the physiological expression of the membrane phospholipids fatty acid turnover.     

Incorporation into liver microsomal lipids of linoleic and stearic acids and of their respective products of delta 6 and delta 9 desaturation, gamma-linolenic and oleic acids: effect of age and of blackcurrant seed oil.

The incorporation of [1-14C]linoleic and [1-14C]stearic acid and of their delta 6 and delta 9 desaturation products (gamma-linolenic and oleic acids, respectively) into different classes of lipids was studied in liver microsomes of rats in function of the diet (blackcurrant seed oil diet, containing gamma-linolenic acid, versus control diet) and in function of age (3, 6 and 9 months). After delta 6 desaturation, total radioactivity was distributed between phospholipids, especially phosphatidylcholine, and neutral lipids. The desaturation product, gamma-linolenic acid, was totally recovered in the phospholipid fraction. Blackcurrant seed oil, which decreased the rate of delta 6 desaturation in 6- and 9-month-old rats, also decreased the incorporation of radioactivity in total phospholipids, especially in phosphatidylcholine. At 6 months of age, after delta 9 desaturation, the majority of radioactivity was recovered in neutral lipids principally as oleic acid, the desaturation product. The precursor, stearic acid, was highly incorporated into phospholipids, especially in rats on a diet of blackcurrant seed oil.     

Cytidylyltransferase translocation onto endoplasmic reticulum and increased de novo synthesis without phosphatidylcholine accumulation in Krebs-II ascite cells.

Addition of oleic acid to Krebs-II cells stimulated by 9-fold [3H]choline incorporation into choline glycerophospholipids without affecting the selective incorporation of the precursor into diacyl subclass (90% of total [3H]choline glycerophospholipids). The total activity of cytidylyltransferase (E.C. 2.7.7.15), the regulatory enzyme of choline glycerophospholipid synthesis, was increased in the particulate fraction at the expense of cytosol. Free [3H]oleic acid was also associated with the particulate fraction. Subcellular fractionation of membranes on Percoll gradient, indicated that the endoplasmic reticulum, which contained 90% of total cell free oleic acid, was the unique target for the translocation of cytidylyltransferase. [3H]oleic acid was incorporated almost exclusively into phosphatidylcholine and corresponded to a synthesis of 9 nmol/h per 10(6) cells. Based on [3H]choline incorporation a net synthesis of 22 nmol/h per 10(6) cells was determined. However, oleic acid treatment did not change the total amount of phosphatidylcholine (45 nmol/10(6) cells) and other phospholipids; also no modification in the subcellular distribution of phospholipids was observed. It is concluded that the stimulation of the de novo synthesis of phosphatidylcholine which involves translocation of cytidylyltransferase onto the endoplasmic reticulum, is accompanied by a renewal of their polar head group. Also exogenous oleic acid induces an enhanced fatty acid turnover, highly specific for phosphatidylcholine. Therefore, Krebs-II cells exhibited a high degree of regulation of their phosphatidylcholine content, suggesting a parallel stimulation of both synthesis and degradation.     

Acylation of lysolecithin in the intestinal mucosa of rats

1. The presence of an active acyl-CoA-lysolecithin (1-acylglycerophosphorylcholine) acyltransferase was demonstrated in rat intestinal mucosa. 2. ATP and CoA were necessary for the incorporation of free [1-(14)C]oleic acid into lecithin (phosphatidylcholine). 3. The reaction was about 20 times as fast with [1-(14)C]oleoyl-CoA as with free oleic acid, CoA and ATP. 4. With 1-acylglycerophosphorylcholine as the acceptor, both oleic acid and palmitic acid were incorporated into the beta-position of lecithin; the incorporation of palmitic acid was 60% of that of oleic acid. 5. Of the various analogues of lysolecithin tested as acyl acceptors from [1-(14)C]oleoyl CoA, a lysolecithin with a long-chain fatty acid at the 1-position was most efficient. 6. The enzyme was mostly present in the brush-border-free particulate fraction of the intestinal mucosa. 7. Of the various tissues of rats tested for the activity, intestinal mucosa was found to be the most active, with testes, liver, kidneys and spleen following it in decreasing order.     

Incorporation of 1-(14)C linoleic acid in rat liver nuclei and chromatin fractions

The incorporation of 1-(14)C linoleic acid in several chromatin fractions of rat liver nuclei was investigated using two different procedures: (1) rat liver nuclei were incubated with ATP, CoASH, Mg(++) and 1-(14)C linoleic acid. After 40 min at 37 degrees C the chromatin obtained by sonication of nuclei suspended in 0.25 M sucrose was fractionated by differential sedimentation; (2) chromatin fractions obtained by differential sedimentation were incubated separately with ATP, CoASH, Mg(++) and 1-(14)C linoleic acid 40 min at 37 degrees C in order to characterize the fatty acid incorporation in isolated chromatin. A comparative study of the incorporation of 1-(14)C linoleic acid in microsomes and nuclei isolated from rat liver is also presented for the purpose of comparison. Linoleic acid was incorporated into nuclear lipids as well as in chromatin fractions. The fatty acid incorporation was stimulated considerably in the acylation system when compared to control, it appears to be highly dependent on the state of condensation of chromatin, being barely detectable in the lowest density fraction. The major proportion of 1-(14)C linoleic acid was found in phospholipids and in a lesser proportion it remained esterified to triglycerides and cholesteryl esters. The distribution of radioactivity in different classes of phospholipids present in microsomes and nuclei isolated from rat liver, showed a similar profile of distribution. The major proportion of radioactivity, approximately 50% was found in phosphatidylcholine and in a lesser proportion in sphingomyelin, phosphatidylserine and phosphatidylethanolamine. When chromatin fractions were incubated separately, it was observed that the major proportion of 1-(14)C linoleic acid in phospholipids was found in heavy chromatin fractions whereas low density chromatin fraction only incorporated in a lesser proportion.     

Eicosapentaenoic acid reduces hepatic synthesis and secretion of triacylglycerol by decreasing the activity of acyl-coenzyme A:1,2-diacylglycerol acyltransferase

The mechanism for the reduced hepatic production of triacylglycerol in the presence of eicosapentaenoic acid was explored in short-term experiments using cultured parenchymal cells and microsomes from rat liver. Oleic, palmitic, stearic, and linoleic acids were the most potent stimulators of triacyl[3H]glycerol synthesis and secretion by hepatocytes, whereas erucic, alpha-linolenic, gamma-linolenic, arachidonic, docosahexaenoic, and eicosapentaenoic acids (in decreasing order) were less stimulatory. There was a linear correlation (r = 0.85, P less than 0.01) between synthesis and secretion of triacyl[3H]glycerol for the fatty acids examined. The extreme and opposite effects of eicosapentaenoic and oleic acids on triacylglycerol metabolism were studied in more detail. With increasing number of free fatty acid molecules bound per molecule of albumin, the rate of synthesis and secretion of triacyl[3H]glycerol increased, most markedly for oleic acid. Cellular uptake of the two fatty acids was similar, but more free eicosapentaenoic acid accumulated intracellularly. Eicosapentaenoic acid caused higher incorporation of [3H]water into phospholipid and lower incorporation into triacylglycerol and cholesteryl ester as compared to oleic acid. No difference was observed between the fatty acids on incorporation into cellular free fatty acids, monoacylglycerol and diacylglycerol. The amount of some 16- and 18-carbon fatty acids in triacylglycerol was significantly higher in the presence of oleic acid compared with eicosapentaenoic acid. Rat liver microsomes in the presence of added 1,2-dioleoyl-glycerol incorporated eicosapentaenoic acid and eicosapentaenoyl-CoA into triacylglycerol to a lesser extent than oleic acid and its CoA derivative. Decreased formation of triacylglycerol was also observed when eicosapentaenoyl-CoA was given together with oleoyl-CoA, whereas palmitoyl-CoA, stearoyl-CoA, linoleoyl-CoA, linolenoyl-CoA, and arachi-donoyl-CoA had no inhibitory effect. In conclusion, inhibition of acyl-CoA:1,2-diacylglycerol O-acyltransferase (EC 2.3.1.20) by eicosapentaenoic acid may be important for reduced synthesis and secretion of triacylglycerol from the liver.     

t-Butyl hydroperoxide alters fatty acid incorporation into erythrocyte membrane phospholipid

Because the ability of cells to replace oxidized fatty acids in membrane phospholipids via deacylation and reacylation in situ may be an important determinant of the ability of cells to tolerate oxidative stress, incorporation of exogenous fatty acid into phospholipid by human erythrocytes has been examined following exposure of the cells to t-butyl hydroperoxide. Exposure of human erythrocytes to t-butyl hydroperoxide (0.5-1.0 mM) results in oxidation of glutathione, formation of malonyldialdehyde, and oxidation of hemoglobin to methemoglobin. Under these conditions, incorporation of exogenous [9,10-3H]oleic acid into phosphatidylethanolamine is enhanced while incorporation of [9,10-3H]oleic acid into phosphatidylcholine is decreased. These effects of t-butyl hydroperoxide on [9,10-3H]oleic acid incorporation are not affected by dissipating transmembrane gradients for calcium and potassium. When malonyldialdehyde production is inhibited by addition of ascorbic acid, t-butyl hydroperoxide still decreases [9,10-3H]oleic acid incorporation into phosphatidylcholine but no stimulation of [9,10-3H]oleic acid incorporation into phosphatidylethanolamine occurs. In cells pre-treated with NaNO2 to convert hemoglobin to methemoglobin, t-butyl hydroperoxide reduces [9,10-3H]oleic acid incorporation into phosphatidylcholine by erythrocytes but does not stimulate [9,10-3H]oleic acid incorporation into phosphatidylethanolamine. Under these conditions oxidation of erythrocyte glutathione and formation of malonyldialdehyde still occur. These results indicate that membrane phospholipid fatty acid turnover is altered under conditions where peroxidation of membrane phospholipid fatty acids occurs and suggest that the oxidation state of hemoglobin influences this response.     

Comparison of triglyceride and phospholipid synthesis in isolated Wistar rat liver perfused with high quantities of oleic acid and glycerol

In a recirculating system, [9,10(-3)H2] oleic acid (346 mumol) and [1-14C] glycerol (115 mumol) are perfused into livers of 18-h fasting Wistar rats. These precursors are incorporated in same amounts into triacylglycerols, and in amounts growing up with the duration of the experiment (5 to 120 min). Their incorporation is slight into phospholipids. However, during the experiment, the increase of 3H/14C ratio of every acylglycerols shows that more lipids are synthetized in the acylation way than in the de novo way. The only synthesis of phospholipids, studied in the two ways, seems to be regulated, unlike the one of triacylglycerols in those experimental conditions.     

In vitro lipid metabolism in the rat pancreas. I. Basal lipid metabolism.

1. The in vitro basal lipid metabolism of rat pancreatic fragments was compared with that in adipose tissue fragments and liver slices. 2. [1-14C]Acetate added to the media was mostly incorporated into palmitic acid and to a lesser extent into oleic acid. In addition, pancreatic tissue exhibited a marked capacity for elongation of polyunsaturated fatty acids by [1-14C]acetate and resulting desaturation when compared to adipose tissue and liver. 3. Data obtained in the presence of [U-14C]glucose, [1-14C]palmitate and 3H20 indicate that acetyl-CoA derived from glucose and from beta-oxidation of fatty acids contributed to de novo lipogenesis. 4. Oxidation of [1-14C]palmitic acid was 9-13 times higher in the pancreas than in adipose tissue or liver when expressed on a wet weight basis. 5. The fatty acid moiety of pancreatic glycerolipids could be derived from de novo synthesis, fatty acids added to the medium, or from fatty acids formed from the hydrolysis of endogenous lipids. The glycerol moiety could be derived either from glucose, or directly from glycerol through participation of glycerol kinase.     

Lysophosphatidylserine dependent incorporation of acyl CoA into phospholipids in rat brain microsomes

[¹⁴C]OleoylCoA was incorporated into phosphatidylinositol 4$\text{1}\text{2}$ times more efficiently than into phosphatidylserine in rat brain and liver microsomes when incubated with various levels of 1-acyl-sn-glycero-3-phosphoserine. In contrast, 1-acyl-sn-glycero-3-phosphocholine dependent incorporation of oleoylCoA was only into phosphatidylcholine. When [l-³H]serine labeled 1-acyl-sn-glycero-3-phosphoserine was used as the labeled substrate, no phosphatidylserine synthesis could be detected in rat brain microsomes. OleoylCoA incorporation in phospholipids in the presence of lysophosphatidylserine was primarily at the 2-position while stearoylCoA was incorporated at the 1-position. These results are interpreted to suggest that there is no acylCoA:1-acyl-sn-glycero-3-phosphoserine acyltransferase in rat brain microsomes and the lysophosphatidylserine dependent position-specific incorporation of acylCoA into various phospholipids may be due to an exchange reaction. A simple highly reproducible one dimensional thin-layer chromatographic system is described for the separation of all the major phospholipids of brain and liver.     

Effect of Light on the Metabolism of Lipids in the Rat Retina

The effect of light on the in vitro incorporation of a variety of radioactive precursors into glycerolipids was tested in isolated retinas of albino rats. There was an increase in the incorporation of [2-3H]myo-inositol, 32Pi, [2-3H]glycerol, and [methyl-3H]choline into retinal phospholipids in light compared to that in darkness. [2-3H]myo-Inositol was incorporated primarily into phosphatidylinositol. 32Pi was incorporated primarily into the phosphoinositides, although there were significant increases in the specific activities of all retinal phospholipids in light compared to those in darkness. Likewise, [2-3H]glycerol incorporation into all retinal phospholipids and diglycerides was greater in light than in the dark. There was no effect of light on the incorporation of [2-3H]ethanolamine into phosphatidylethanolamine or of [3-3H]serine into phosphatidylserine, although these phospholipids were labeled to a greater extent in light with [2-3H]glycerol. There was no effect of light on the incorporation of [3H]palmitic acid into diglycerides and phospholipids, with the exception of phosphatidylinositol. Light also had no effect on the uptake of [2-3H]glycerol, [2-3H]inositol, or [methyl-3H]choline into the retina. We conclude from these studies that light stimulates the phosphoinositide effect in the rat retina. Although some of the results are consistent with a stimulation of de novo synthesis of all lipid classes, our studies with [3H]palmitate, [2-3H]ethanolamine, and [3-3H]serine do not support this conclusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Quantitative properties and biosynthesis of phospholipids in rat embryonic tissues in the process of development

The content of lipid phosphorus and the rate of [1-14C]palmitate incorporation into individual phospholipids of rat embryonic liver, kidney, spleen, brain, and placenta at different stages of prenatal development were studied. It was shown that the level of neutral phospholipids at all stages is much higher than that in acid fractions; however, the rate of the acid fraction exchange is 10 times higher depending on the age of the embryos. The specific radioactivity of individual fractions of embryonic rat tissue largely exceeds that in adult animals.     

Biosynthesis of mitochondrial phospholipids using endogenously generated diglycerides.

When isolated mitochondria or microsomes from rat liver were treated with phospholipase C, the incorporation of radioactive phospholipid precursors was markedly enhanced, presumably as a result of production of diglycerides by hydrolysis of endogenous phospholipids. Incorporation of CDP[14C]choline into lecithin in rat liver or BHK-21 mitochondria could be attributed to residual contamination from elements of the endoplasmic reticulum, with added diglycerides or with endogenous diglycerides produced by the phospholipase C treatment. A similar stimulation of [gamma32P]ATP incorporation into phospholipids was observed with exogenous or endogenous diglycerides, but the mitochondrial diglyceride kinase in either case was also related to the degree of microsomal contaminants. It was concluded that previous studies showing negligible capacity of mitochondria for lecithin biosynthesis de novo were not explainable on the basis of limited accessibility of added diglycerides, and that formation of phosphatidic acid by diglyceride kinase was not of significance in rat liver mitochondria.     

Biosynthetic incorporation of cis-parinaric acid into radioactive sn-3-phosphatidic acid

Isolated guinea pig liver microsomal membranes catalyzed the incorporation of naturally occurring cis-parinaric acid into sn-3-[U-14C]glycerophosphate. This resulted in the formation of sn-3-[14C](parinaroyl)phosphatidic acid, which was isolated by Chelex-100 and DEAE-cellulose column chromatography and further purified by Sephadex-G 25. The sn-3-[14C](parinaroyl)phosphatidic acid thus obtained exhibited absorption and fluorescence spectra substantially different from the cis-parinaric acid. Distribution of the incorporated cis-parinaric acid between the hydroxyl groups of biosynthesized sn-3-[14C]phosphatidic acid was determined by degradation with Crotalus adamanteus venom. This established that the major portion of the incorporated cis-parinaric acid esterified the secondary hydroxyl group in the sn-3-[14C]phosphatidic acid, while the primary hydroxyl group was esterified to a significantly lesser degree. The similarity between the biochemical incorporation of isomeric doxyl stearic acids into lipids of biological membranes and that of cis-parinaric acid into sn-3-phosphatidic acid described in this communication are discussed in relation to the possible use of these probes in studies of intact biological membranes.     

Effect of NK-104, a new synthetic HMG-CoA reductase inhibitor, on triglyceride secretion and fatty acid oxidation in rat liver.

For the investigation of the mechanism responsible for the hypotriglyceridemic effect of NK-104, a new synthetic inhibitor of HMG-CoA reductase, the rate-limiting enzyme for cholesterol synthesis, isolated rat liver was perfused with or without NK-104 in the presence of exogenous [1-(14)C]oleic acid substrate. Addition of NK-104 tended to increase the ketone body production while it caused a significant decrease in the secretion rate of triglyceride by the perfused liver without affecting uptake of exogenous [1-(14)C]oleic acid. The inhibitor also significantly decreased hepatic triglyceride concentration. The altered triglyceride secretion was accompanied by a concomitant decreased incorporation of exogenous [1-(14)C]oleate into triglyceride. The conversion of exogenous [1-(14)C]oleic acid substrate indicated an inverse relationship between the pathways of oxidation and esterification. No effect of NK-104 on hepatic secretion of cholesterol was observed. These results suggest that NK-104 exerts its hypotriglyceridemic action, primarily by diverting the exogenous free fatty acid to the pathways of oxidation at the expense of esterification.     

Fatty acid uptake and catecholamine-stimulated phospholipid metabolism in immortalized airway epithelial cells established from primary cultures

The incorporation of [14C]oleic and [14C]linoleic acid into phospholipids and neutral lipids was compared in two recently immortalized airway epithelial cell lines. In addition, the effects of adrenergic stimulation on phospholipid turnover was examined. Both cell lines readily incorporated the fatty acids into all phospholipid and neutral lipid fractions. Isoproterenol (1 microM) induced Ca2+ transients in both cell lines, indicating a functional beta-adrenergic response. Epinephrine (10 microM; 15 min) stimulation of cells prelabeled with [14C]linoleic acid increased the percentage of label in phosphatidylcholine in one cell line. Lipid metabolism can now be extensively studied in human airway epithelia.     

INCORPORATION OF [1-14C]OLEIC ACID AND [1-14C]ARACHIDONIC ACID INTO LIPIDS IN THE SUBCELLULAR FRACTIONS OF MOUSE BRAIN

Abstract— The distribution of radioactivity among lipids of subcellular membrane fractions was examined after intracerebral injections of [1-¹⁴C]oleic and [1-¹⁴C]arachidonic acids. Labelled free fatty acids were distributed among the synaptosomal-rich, microsomal, myelin and cytosol fractions at 1 min after injection. However, incorporation of the fatty acids into phospholipids and trïacylglycerols after pulse labelling occurred mainly in the microsomal and synaptosomal-rich fractions. With both types of labelled precursors, there was a higher percentage of radioactivity of diacyl-glycerophosphoryl-inositols in the synaptosomal-rich fraction as compared to the microsomal fraction. Radioactivity of [1-¹⁴C]oleic acid was effectively incorporated into the triacylglycerols in the microsomal fraction whereas radioactivity of the [1-¹⁴C]arachidonic acid was preferentially incorporated into the diacyl-glycerophosphorylinositols in the synaptosomal-rich fraction. Result of the study indicates that synaptosomal-rich fraction in brain is able to metabolize long chain free fatty acids in vivo and to incorporate these precursors into the membrane phosphoglycerides.     

Biosynthetic Incorporation of CIS-Parinaric Acid Into Radioactive SN-3-Phosphatidic Acid

Isolated guinea pig liver microsomal membranes catalyzed the incorporation of naturally occurring cis-parinaric acid into sn-3-[U-¹⁴ C]glycerophosphate. This resulted in the formation of sn-3-[¹⁴C](parinaroyl)phosphatidic acid, which was isolated by Chelex-100 and DEAE-cellulose column chromatography and further purified by Sephadex-G 25. The sn-3-[¹⁴C](parinaroyl)phosphatidic acid thus obtained exhibited absorption and fluorescence spectra substantially different from the cis-parinaric acid. Distribution of the incorporated cis-parinaric acid between the hydroxyl groups of biosynthesized sn-3-[¹⁴C]phosphatidic acid was determined by dearadation with Crotalus adamateus venom. This established that the major portion of the incorporated cis-panaric acid esterified the secondary hydroxyl group in the sn-3-[¹⁴C] phosphatidic acid, while the primary hydroxyl group was esterified to a significantly lesser degree. The similarity between the biochemical incorporation of isomeric doxyl stearic acids into lipids of biological membranes and that of cis-parinaric acid into sn-3-phosphatidic acid described 1n this communication are discussed in relation to the possible use of these probes in studies of intact biological membranes.     

Characterization and metabolism of ovine foetal lipids

1. Total phospholipid concentrations in liver, kidney and brain of the 140-day ovine foetus were only half of those in comparable maternal tissues. 2. Phosphatidylcholine was the predominant phospholipid in all foetal tissues examined. The most striking difference between foetal and maternal tissues in individual phospholipids was in the heart; foetal heart contained more ethanolamine plasmalogen than choline plasmalogen, whereas in adult tissue the concentration of these was reversed. Sphingomyelin content of foetal brain was only one-sixth of that of maternal brain tissue. 3. Oleic acid (18:1) was the predominant acid in the phospholipid extracted from foetal tissues, except in brain where palmitic acid (16:0) was slightly higher. In phospholipids from adult tissues there was a higher proportion of unsaturated fatty acids (linoleic acid, 18:2, and linolenic acid, 18:3) and a correspondingly lower proportion of oleic acid (18:1). The distribution of fatty acids in the neutral lipid fraction of foetal and maternal tissues was very similar; oleic acid (18:1) was generally the principal component. 4. (14)C derived from [U-(14)C]-glucose and [U-(14)C]fructose infused into the foetal circulation in utero was incorporated into the neutral lipids and phospholipids of heart, liver, kidney, brain and adipose tissue. 5. Phospholipid analysis revealed that the specific activity of phosphatidic acid was higher in liver than in other tissues. The specific activity of phosphatidylethanolamine was less than that of phosphatidylcholine in heart, but in other tissues they were about the same. The specific activities of phosphatidylinositol and phosphatidic acid in brain were very similar and were higher than the other components. The specific activity of phosphatidylserine was highest in liver and brown fat. 6. The pattern of incorporation of (14)C derived from [(14)C]glucose and [(14)C]fructose into foetal neutral lipids was similar. Diglyceride accounted for most of the radioactivity in brain, whereas triglyceride had more label in heart, liver, kidney and fat.     

Phospholipid metabolism in Ehrlich ascites tumor cells. I. Turnover rate of phosphatidylinositol.

1. Radioactive precursors, 32 PI, [1-14C]glycerol, and [1-14C]acetate, were individually injected into the peritoneal cavity of mice bearing Ehrlich ascites tumor, and the rates of incorporation into phospholipid fraction of Ehrlich ascites tumor cells were estimated. Although no distinct difference in specific activities was observed between phosphatidylinositol and other phospholipid classes as regards the incorporation of [1-14C]acetate of [1-14C]glycerol, a higher rate of incorporation of 32Pi into phosphatidylinositol was observed. The specific activity of phosphatidylinositol reached more than ten times that of phosphatidylcholine in the first hour. 2. The radioactivities incorporated into the phospholipids of Ehrlich ascites tumor cells and liver were estimated after simultaneous injection 32Pi and [2-3H]inositol. The incorporation of 32Pi into phosphatidylinositol of liver was similar in specific activity to those of other phospholipids. The ratio (3H/32Pi) of phosphatidylinositol only slightly in the ascites tumor cells, while an appreciable decrease of the ratio was observed in the liver during the first 3 hr. 3. These results suggest that phosphatidylinositol synthesis through pathways other than de novo synthesis is rapid in ascites tumor cells.