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PubMed1966

Studies on the respiratory metabolism of isolated human adipose cells.

1. Some metabolic characteristics of fat cells isolated from 50 patients were examined. 2. The respiratory activity of human fat cells was of the same order of magnitude as cells obtained from the rat, whether the comparison was based on the molar triglyceride content of cells or the nitrogen content of tissue. 3. There was no difference in the respiratory metabolism of fat cells isolated from three separate age groups: 20-40, 40-60 and 60-80 years. 4. The respiratory activity of human adipose cells was partially inhibited by malonate (0.1m), arsenite (1mm) and iodoacetate (1mm). 5. Oxygen consumption by human adipose cells could not be stimulated by adding glucose or glucose plus palmitic acid to the medium. However, stimulation of oxygen uptake with these substrates was observed after the tissue had been preincubated for 5hr. in a bicarbonate buffer. 6. After the tissue had been preincubated for 5hr., there was a linear relationship between the oxygen uptake by isolated cells and the amount of oleic acid added to the incubation medium. Stimulation of oxygen uptake by oleic acid (0.95mumole/ml.) was dependent on the presence of glucose (5.6mm) in the incubation medium. 7. Of the total [1-(14)C]palmitic acid metabolized by human adipose cells, over 99.8% of the radioactivity was recovered in the neutral-lipid fraction and less than 0.2% in carbon dioxide. Under conditions where oxygen uptake is stimulated by [(14)C]-palmitic acid, the radioactivity of the 1,2-diglyceride pool increased 20-fold.

Adipose Tissue↗
PubMed1966

The biosynthesis of glycerides by mitochondria from rat liver. The requirement for a soluble protein.

1. The synthesis of glycerides from l-3-glycerophosphate and palmitic acid by mitochondrial preparations from rat liver was shown to be stimulated markedly by a soluble factor from the supernatant fraction of the liver. 2. That the soluble factor was a protein was indicated by its inactivation after treatment with papain and after boiling for 3min. at 100 degrees , its precipitation by ammonium sulphate and its behaviour on Sephadex G-200. The soluble factor was purified by ammonium sulphate fractionation and gel filtration. 3. Bovine serum albumin and lipoprotein fractions from rat and human serum also stimulated glyceride biosynthesis but the stimulations were one-twentieth to one-third of that obtained with the soluble factor. 4. The function of the soluble factor could not be explained by assuming a leakage of acyl-CoA synthetase, phosphatidate phosphatase or diglyceride acyltransferase from the mitochondria into the supernatant during preparation of the mitochondrial fraction. 5. Palmitic acid, in the presence of the soluble factor and optimum amounts of ATP and CoA, was a more effective substrate than palmitoyl-CoA or palmitoylcarnitine for the biosynthesis of glycerides by mitochondria.

Acyltransferases↗
PubMed1967

Lipid composition of human serum lipoproteins.

1. The lipid compositions of the low-density lipoproteins, the high-density lipoproteins and the ultracentrifugal residue of human serum are presented, with emphasis on certain lipoprotein classes and lipid components not previously described. 2. Except for the lipoproteins with the lowest and highest densities, there is a trend for stepwise successive increase or, respectively, decrease in the relative amounts of the main constituents of lipoproteins. 3. High-density lipoprotein-2 and high-density lipoprotein-3 have different amounts of certain lipids; high-density lipoprotein-2 has relatively more free cholesterol and sphingomyelin; high-density lipoprotein-3 has more free fatty acids, diglycerides and ceramide monohexosides. 4. All the lipoproteins contain hydrocarbons of the alkane series. The greatest amount, which averages 4.4% of total lipid extracted, is in the ultracentrifugal residue; n-alkanes comprise 18-50% of the hydrocarbons. 5. All the lipoproteins contain ceramide monohexosides. The highest relative contents of these glycolipids are in high-density lipoprotein-3 and in the ultracentrifugal residue. 6. The ultracentrifugal residue contains 55% of the total quantity of free fatty acids present in serum. The remaining free fatty acids are distributed among the other lipoprotein classes. 7. The choline-containing phospholipids (phosphatidylcholine, lysophosphatidylcholine and sphingomyelin) comprise about 90% of the phospholipids in all the lipoprotein classes except the low-density lipoprotein-2, which contains about 80% of these phospholipids. 8. The presence of a large amount of lysophosphatidylcholine in the ultracentrifugal residue and the successive decrease of sphingomyelin from the low-density lipoprotein-1 to the ultracentrifugal residue was confirmed. 9. The low-density lipoprotein-2 and the ultracentrifugal residue are characterized by relatively high contents of the lower glycerides.

Adult↗
PubMed1967

Concentrations of glycerides and phospholipids in rat heart and gastrocnemius muscles. Effects of alloxan-diabetes and perfusion.

1. Methods are described for the extraction of lipid and assay of mono-, di- and tri-glyceride glycerol and phospholipid phosphorus in rat heart and gastrocnemius muscles. 2. In hearts from normal animals, concentrations found were: monoglyceride, 0.6; diglyceride, 0.1; triglyceride, 12.6mumoles of glyceride glycerol/g. of dry muscle; phospholipid, 171mug.atoms of phospholipid phosphorus/g. of dry muscle. Concentrations of glycerides in gastrocnemius muscle were similar to heart muscle but those of phospholipids were lower (64mug.atoms of phospholipid phosphorus/g. of dry muscle). 3. Alloxan-diabetes increased the concentration of triglyceride in the muscles twofold. This increase was shown to be dependent in the heart on the availability of growth hormone and cortisol but not on the availability of dietary lipid. Total glyceride in the heart was increased after 48 and 72hr. starvation but not after 96hr. Changes in glyceride concentration seen in starvation and diabetes were not associated with significant changes in phospholipid concentration. It is suggested that mobilization of free fatty acids in diabetes leads to the synthesis of additional glyceride in muscle. 4. The possible contribution of glyceride fatty acid in the heart to respiration during perfusion has been calculated from the net loss of glyceride during perfusion, and also from the relative rates of lipolysis and esterification and compared with oxidation of fatty acid required for the balance of oxygen consumption (oxygen not utilized in the oxidation of glucose or glycogen glucose). In the normal or diabetic heart perfused with glucose and insulin the breakdown of glyceride can account for the balance of oxygen consumption. In the normal heart perfused without substrate the balance of oxygen consumption is not entirely accounted for by the breakdown of glyceride.

Animals↗
PubMed1967

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.

Animals↗
PubMed1967

Regulation of triglyceride synthesis in the parturient guinea-pig mammary gland.

1. The specific activity of the enzyme palmitoyl-CoA-l-glycerol 3-phosphate palmitoyltransferase (EC 2.3.1.15) in the mammary tissue of guinea pigs has been shown to increase 37-fold at parturition. 2. Increases also occur in tissue concentrations of glycerol 3-phosphate, CoA and free fatty acid, but not in that of acid-insoluble CoA. 3. The isolation and fatty acid composition of plasma triglyceride and of mammary-tissue free fatty acid, diglyceride and triglyceride are described. 4. The findings are discussed in relation to the regulation of milk fat synthesis.

Acyltransferases↗
PubMed1967

The aminoethylphosphonate-containing lipids of rumen protozoa.

1. A method is presented for identifying and estimating the aminoethylphosphonate (ciliatine)-containing phospholipids in a complex mixture. 2. Evidence was obtained that the phospholipids of a pure culture of Entodinium caudatum and a mixed rumen protozoa sample contain diglyceride ciliatine, and a plasmalogen ciliatine was detected in the latter. 3. A ninhydrin-positive sphingolipid was isolated from rumen protozoa. Although chromatographically homogeneous on silica gel it contains two components, which were provisionally identified as ceramide ciliatine and ceramide phosphorylethanolamine. 4. A detailed phospholipid analysis of E. caudatum and rumen protozoa is presented. They contain no phosphatidylserine or cardiolipin, but an unidentified phosphoglyceride containing a zwitterionic amino acid is present.

Animals↗
PubMed1967

The structure and possible function of the glycolipid from Staphylococcus lactis I3.

1. The total lipid was extracted from Staphylococcus lactis I3 with chloroform-methanol mixtures and the glycolipid component was isolated by chromatography on silicic acid. 2. Saponification yielded a non-crystalline glycoside for which the structure O-beta-d-glucopyranosyl-(1-->6)-O-beta-d-glucopyranosyl-(1-->1)-d-glycerol has been established by chemical degradations and by comparison with synthetic material. 3. The role of the glycosyl diglycerides in bacterial membranes is discussed.

Chromatography↗
PubMed1968

The chemical composition of the membranes of protoplasts and L-forms of Staphylococcus aureus.

Membrane fractions were prepared from Staphylococcus aureus H and 100 after dissolution of the cell walls by a lytic enzyme from Streptomyces griseus. Membranes were also prepared from the L-forms derived from the same strains. The membranes were analysed for protein, lipid, carbohydrate and RNA contents, and the fatty acid composition of the lipids was determined. A branched-chain saturated C(15) acid was the major component in all samples, and the correspondence between L-forms and parent bacteria was fairly close. The lipids were separated into non-polar-lipid, glycolipid and phospholipid fractions; the L-forms contained a little more neutral lipid and much more glycolipid than the parent bacteria. In all membranes the glycolipid, which accounted for all the carbohydrate present, was a diglucosyl diglyceride. The major phospholipids of the protoplast membranes were phosphatidylglycerol and some lipoamino acids (lysine and a little alanine). On the other hand, diphosphatidylglycerol was the chief phospholipid found in L-form membranes.

Amino Acids↗
PubMed1968

The diphosphoinositide kinase of rat brain.

1. The supernatant fraction of adult rat brain contains a diphosphoinositide kinase. 2. Formation of triphosphoinositide by the enzyme in the presence of ATP and Mg(2+) ions was shown with labelled ATP or labelled diphosphoinositide. 3. The kinase was also activated by Ca(2+), Mn(2+) and Co(2+) ions, but to a smaller extent than by Mg(2+) ions. 4. In the presence of optimum Mg(2+) ion concentration the enzyme was inhibited by Ca(2+) ions. 5. Activity did not depend on thiol groups and the pH optimum was 7.3. 6. The dialysed supernatant fraction had no diglyceride kinase activity and negligible phosphatidylinositol kinase activity. 7. Triphosphoinositide phosphomonoesterase was present but showed little activity under the conditions used to assay the kinase. 8. Diphosphoinositide kinase was purified by ammonium sulphate fractionation, ethanol treatment and chromatography on Sephadex G-200. 9. This purification removed much of the triphosphoinositide phosphomonoesterase.

Acetylcholine↗
PubMed1968

Lipid metabolism in the testis of the ram.

1. Analysis of rams testes revealed that phosphatidylcholine was the major phospholipid and accounted for about 40% of the total. Only small amounts of choline plasmalogen were present. 2. The ratio of phosphatidylcholine to choline plasmalogen in the testis was very different from that occurring in the spermatozoa. This result was in contrast with those for rat testis and rat spermatozoa (obtained from the head of the epididymis), where the ratio of the two lipids was very similar. 3. Infusions of [(32)P]orthophosphate into the testicular artery of rams resulted in incorporation of radioactivity into most phospholipids; phosphatidylinositol labelling accounted for 68% and 39% of the radioactivity after infusions lasting 3hr. and 5hr. respectively. 4. With the exception of phosphatidic acid the specific radioactivity of phosphatidylinositol was higher than that of any other lipid. 5. After the infusion of [U-(14)C]glucose, triglycerides accounted for about 60% of the radioactivity in testicular neutral lipids, whereas diglycerides had only about 15% of the radioactivity. 6. Palmitic acid (16:0) was the major component both in neutral lipids and phospholipids of ram testes. 7. The effects of gonadotrophic hormones (luteinizing hormone and follicle-stimulating hormone) on the incorporation of [(32)P]orthophosphate into total testicular phospholipids in vivo were also examined.

Animals↗
PubMed1968

Composition of the protoplast membrane from Saccharomyces cerevisiae.

1. Protoplasts of Saccharomyces cerevisiae N.C.Y.C. 366 were prepared by incubating washed exponential-phase cells in buffered mannitol (0.8m) containing 10mm-magnesium chloride and snail gut juice (about 8mg. of protein/ml. of reaction mixture). Protoplast membranes were obtained by bursting protoplasts in ice-cold phosphate buffer (pH7.0) containing 10mm-magnesium chloride. 2. Protoplast membranes accounted for 13-20% of the dry weight of the yeast cell. They contained on a weight basis about 39% of lipid, 49% of protein, 6% of sterol (assayed spectrophotometrically) and traces of RNA and carbohydrate (glucan+mannan). 3. The principal fatty acids in membrane lipids were C(16:0), C(16:1) and C(18:1) acids. Whole cells contained a slightly greater proportion of C(16:0) and a somewhat smaller proportion of C(18:1) acids. Membrane and whole-cell lipids included monoglycerides, diglycerides, triglycerides, sterols, sterol esters, phosphatidylcholine, lysophosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol+phosphatidylserine. Phosphorus analyses on phospholipid fractions from membranes and whole cells showed that membranes contained proportionately more phosphatidylethanolamine and phosphatidylinositol+phosphatidylserine than whole cells, which in turn were richer in phosphatidylcholine. Phospholipid fractions from membranes and whole cells had similar fatty acid compositions. 4. Membranes and whole cells contained two major and three minor sterol components. Gas-liquid chromatography, mass spectrometry and u.v. and i.r. spectra indicated that the major components were probably Delta(5,7,22,24(28))-ergostatetraen-3beta-ol and zymosterol. The minor sterol components in whole cells were probably episterol (or fecosterol), ergosterol and a C(29) di-unsaturated sterol. 5. Defatted whole cells contained slightly more glutamate and ornithine and slightly less leucine and isoleucine than membranes. Otherwise, no major differences were detected in the amino acid compositions of defatted whole cells and membranes.

Amino Acids↗
PubMed1968

The metabolism of [Me-14C]choline in the brain of the rat in vivo.

[Me-(14)C]Choline was injected intracerebrally into the adult rat, and its uptake into the lipids and their water-soluble precursors in brain was studied. The radioactivity could be detected only in the choline-containing lipids and was confined to the base choline. The results indicated that initial phosphorylation of the free choline followed by the formation of CDP-choline and the subsequent transfer of the phosphorylcholine to a diglyceride is one of the principal routes by which choline lipids in brain are formed. Further evidence for this was obtained in experiments in which either phosphoryl[Me-(14)C]choline or [(32)P]orthophosphate was injected and the radioactivity in the choline-containing water-soluble and lipidbound components studied.

Animals↗
PubMed1970

Metabolism of endogenous sterol ester by the superovulated rat ovary in vitro.

Sterol, glyceride and phospholipid were found to account for more than 90% (w/w) of the lipid extracted from whole superovulated rat ovaries. These lipids, together with non-esterified fatty acids, were assayed in slices of the tissue after incubation for various times. Whereas the concentrations of triglyceride, diglyceride and phospholipid did not change significantly during incubation, that of sterol ester markedly decreased and those of free sterol, monoglyceride and non-esterified fatty acid increased. Evidence is presented that in this tissue (in contrast with other mammalian tissues) the main endogenous substrate for respiration is fatty acid derived from sterol ester.

Animals↗
PubMed1970

Phosphatidic acid and phosphatidylinositol metabolism in Schizosaccharomyces pombe.

The phospholipid composition of Schizosaccharomyces pombe was not markedly affected by changes in the phosphate concentration of the medium or phase of growth. The major fatty acids in the total lipid extract and purified phosphatidylinositol were palmitic acid and oleic acid. Phosphatidic acid was synthesized by acylation of l-3-glycerophosphate in Schiz. pombe and phosphatidate phosphohydrolase was present. Phosphatidylinositol synthesis from inositol occurred in the absence of CDP-diglyceride. Even with dialysed cell-free preparations, the inositol lipid was synthesized by an apparently energy-independent route, at rates greater than would be required during cell growth. Phosphatidylinositol appeared to be broken down by a phospholipase D. All the enzymes examined were particulate; similar activities were found in Saccharomyces cerevisiae.

Cell-Free System↗
PubMed1971

The metabolism of phosphatidylinositol in the thyroid gland of the pig.

1. The metabolism of phosphatidylinositol in pig thyroid has been investigated as a basis for understanding the specific stimulation of the synthesis of this phospholipid in the gland by thyrotropin. 2. The gland contained an active Ca(2+)-dependent phosphatidylinositol-splitting enzyme with an optimum pH of 5.3-5.5. 3. The major water-soluble product (65%) formed by this catabolic enzyme was not phosphorylinositol but a related compound, which may be a cyclic phosphorylinositol. Both this and phosphorylinositol (35%) were released simultaneously from the phosphatidylinositol substrate. 4. The phosphatidylinositol-splitting enzyme was found almost exclusively in the supernatant fraction obtained by homogenization of the gland. It was not present in the acid-phosphatase-containing particulate fraction. 5. The incorporation of [2-(3)H(1)]inositol into phosphatidylinositol in the presence of either CDP-diglyceride or CTP+ATP was most active in the microsomal fraction. 6. When thyroidal microsomes were labelled with [(3)H]inositol and (32)P, and then incubated with unlabelled inositol, there was a dramatic loss of (3)H labelling from the phosphatidylinositol, which was not accompanied by an equivalent loss of (32)P from the phosphate moiety. This turnover of the inositol moiety required nucleotide coenzymes. It is postulated that the phosphatidylinositol is split into inositol and a phosphorus-containing lipid precursor of the phospholipid that remains on the microsomal membrane and is recycled. 7. Isolated thyroidal mitochondria synthesized phosphatidylinositol from [2-(3)H(1)]inositol only because of their contaminating microsomal component. 8. Some evidence has been obtained of a rapid transfer of phosphatidylinositol molecules from thyroidal microsomes to mitochondria when these were incubated together in the presence of a supernatant fraction. 9. Both phosphatidylinositol breakdown by the supernatant fraction of the gland and synthesis by the microsomes were totally inhibited by 1mm-chlorpromazine. This drug is known to suppress thyrotrophin-induced stimulation of activity in thyroid slices.

Acid Phosphatase↗
PubMed1971

The role of the plasma membrane in fatty acid uptake by rat liver parenchymal cells.

1. Suspensions of isolated rat liver parenchymal cells incorporate [(14)C]palmitic acid into glycerides at about 40% of the rate obtained with liver slices. 2. At short time-intervals most of the incorporation is into phosphatidylcholine and this is recovered mainly in the plasma-membrane fraction. 3. At later times (5min to 2h) the [(14)C]palmitic acid is mainly found in triglyceride, but this is not recovered in the plasma-membrane fraction. 4. Addition of lysophosphatidylcholine increases incorporation of palmitic acid into both phosphatidylcholine and triglyceride, with maximum effect at about 0.1mm. 5. In vivo, 1min after injection of [(14)C]palmitic acid, radioactive phosphatidylcholine is concentrated in the plasma-membrane fraction, but the proportion present in this fraction declines rapidly. 6. The phosphatidylcholine of the plasma-membrane fraction has, at 1min after injection, a specific radioactivity 30-fold greater than that of the whole tissue. 7. This phosphatidylcholine reaches its maximum specific radioactivity before the tissue phosphatidic acid or diglyceride. 8. The phosphatidylcholine of the plasma-membrane fraction has a very rapid turnover. 9. It is proposed that the rapid formation of phospholipids in the plasma membrane is by acylation of their lyso-derivatives and the role of this process in fatty acid uptake is discussed.

Acylation↗
PubMed1973

Hepatic lipid droplets. Isolation, morphology and composition.

The floating lipid layer isolated centrifugation of rat liver was examined for composition and ultrastructure. It was chiefly composed of triglycerides and cholesterol esters plus much smaller amounts of free cholesterol, diglycerides, phospholipid and protein. No free fatty acids were detected. The triglyceride and cholesterol ester fractions consisted mostly of esters of linoleic acid, oleic acid and palmitic acid. Electron micrographs of the floating lipid layer revealed numerous spherical osmiophilic droplets having a mean diameter of 0.5-2mum with a very-thin dense outer coat. Similar structures were observed as organelles in electron micrographs of the intact liver cell. The amount of triglyceride in the layer decreased in rats starved for 72h, but pellet triglyceride (homogenate minus the floating lipid layer) was unchanged. These results suggest that the floating lipid layer is the representative in vitro of lipid-rich organelles which probably function as a depot form of hepatic-cell neutral lipid.

Animals↗