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B Akesson

Publications and source records attributed to B Akesson.

At least 145 records · Page 8Linked to original sources
PubMed1978

Absorption of synthetic, stereochemically defined acylglycerols in the rat.

The stereochemistry of fat digestion and absorption was investigated in rats with thoracic duct fistulas, after feeding synthetic triacylglycerol or alkyldiacylglycerol. After feeding 1,2-dilauroyl-3-oleoyl-sn-glycerol, dilauroyloleoylglycerol and lauroyldioleoylglycerol were the most abundant chyle triacylglycerols. Positional analysis of the fatty acid distribution and the absence of optical activity indicated that the following structures dominated: rac-1,2-dilauroyl-3-oleoylglycerol and rac-1,3-dioleoyl-2-lauroylglycerol. Therefore, the triacylglycerol resynthesized from 2-lauroylglycerol (pre-cursor to 60% of chyle triacylglycerol) and other precursors was essentially racemic. Chyle phospholipids contained largely endogenous fatty acids, and the proportion of lauric acid was very low. A racemic mixture of 1,2-di[3H] oleoyl-3-tetradecyl-sn-glycerol and 1-tetradecyl-2,3-di[12C] oleoyl-sn-glycerol was absorbed to a lower degree than triacylglycerol. The appearace of oleic acid with different labels in chyle and intestinal lipids did not differ, indicating the absence of stereospecificity in fat digestion. Possible explanations for the low absorption are discussed.

Animals↗
PubMed1978

Effects of vitamin B12 deficiency on lipid metabolism of the rat liver and nervous system.

1. Rats bred from vitamin B12-depleted dams were fed on a vitamin B12-deficient diet for 12-15 months and developed a severe vitamin B12 deficiency, as judged from methylmalonic acid excretion and tissue vitamin B12 levels at slaughter. Control rats were supplemented with vitamin B12 in the drinking-water. 2. Neurological signs were recorded after 7 months but the motor nerve conduction velocities remained normal. Neuropathological examination revealed mild changes in the peripheral nerves but no changes in the central nervous system. 3. The amounts of total lipids and phospholipids were normal, but in all examined tissues the proportions of pentadecanoate (C15 fatty acid) and heptadecanoate (C17 fatty acid) were considerably increased in vitamin B12 deficiency. 4. 3H2O was incorporated to the same extent into the fatty acids of nervous tissue from vitamin B12-deficient and control rats after 48 h. Less 3H was found in the liver fatty acids of the vitamin B12-deficient rats. 5. Neurological dysfunction can be demonstrated in the vitamin B12-deficient rat; the relation of the biochemical and neuropathological changes to the neurological signs needs further study.

Animals↗
PubMed1978

Effect of vitamin B12 deficiency on phosphatidylethanolamine methylation in rat liver.

1. In vitamin B12 deficiency the activity of tetrahydropteroylglutamate methyltransferase (EC 2.1.1.13) is depressed and the synthesis of methionine is reduced. Because the methyl group of methionine is largely utilized for the methylation of phosphatidylethanolamine, we investigated the effects of vitamin B12 deficiency on phosphatidylcholine synthesis. 2. The incorporation of injected [14C]formaldehyde into liver phosphatidylcholine was reduced by approximately 50% in vitamin B12-deficient rats. Also the corresponding incorporation of 5-[14C]methyltetrahydrofolic acid tended to decrease. The findings are consistent with a lower conversion of these precursors to methionine. 3. The effect of the deficient methyl-group supply on phosphatidylcholine synthesis was also investigated by the injection of [14C]ethanolamine. The amount (%) of lipid-14C recovered in phosphatidylcholine was significantly reduced in vitamin B12 deficiency. 4. Chemical analysis of liver phospholipids showed that the vitamin B12-deficient rats had a higher proportion of phosphatidylethanolamine and a lower proportion of phosphatidylcholine, indicating that the impaired synthesis of phosphatidylcholine by methylation leads to changes in membrane phospholipid composition.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1977

Effects of analogles of ethanolamine and choline on phospholipid metabolism in rat hepatocytes.

1. Analogues of ethanolamine and choline were incubated with different labelled precursors of phospholipids and isolated hepatocytes and the effects on phospholipid synthesis were studied. 2. 2-Aminopropan-1-ol and 2-aminobutan-1-ol were the most efficient inhibitors of [(14)C]ethanolamine incorporation into phospholipids, whereas the incorporation of [(3)H]choline was inhibited most extensively by NN-diethylethanolamine and NN-dimethylethanolamine. 3. When the analogues were incubated with [(3)H]glycerol and hepatocytes, the appearance of (3)H in unnatural phospholipids indicated that they were incorporated, at least in part, via CDP-derivatives. The distribution of [(3)H]glycerol among molecular species of phospholipids containing 2-aminopropan-1-ol and 1-aminopropan-2-ol was the same as in phosphatidylethanolamine. In other phospholipid analogues the distribution of (3)H was more similar to that in phosphatidylcholine. 4. NN-Diethylethanolamine stimulated both the conversion of phosphatidylethanolamine into phosphatidylcholine and the incorporation of [Me-(14)C]methionine into phospholipids. Other N-alkyl- or NN-dialkyl-ethanolamines also stimulated [(14)C]methionine incorporation, but inhibited the conversion of phosphatidylethanolamine into phosphatidylcholine. This indicates that phosphatidyl-NN-diethylethanolamine is a poor methyl acceptor, in contrast with other N-alkylated phosphatidylethanolamines. 5. These results on the regulation of phospholipid metabolism in intact cells are discussed with respect to the possible control points. They also provide guidelines for future experiments on the manipulation of phospholipid polar-headgroup composition in primary cultures of hepatocytes.

Animals↗
PubMed1977

Phospholipid degradation in isolated rat hepatocytes. Metabolism of intracellularly formed dilinoleoyl-dipalmitoyl- and dimyristoylglycerophosphocholine.

The aim of this work is to describe the role of different phospholipases in hepatic phospholipid catabolism. Therefore isolated rat hepatocytes enriched in labeled dilinoleoyl-, dipalmitoyl- or dimyristoylglycerophosphocholine were prepared by pulse incubation with [3H]glycerol and 14C-labeled fatty acid. The labeled cells were chased up to 4 h in a tracer-free medium and the degradation of different phosphatidylcholines studied. After a 2-h chase about 40% of dilinoleoyl-, 70% of dipalmitoyl- and 30% of dimyristoylglycerophosphocholine were degraded. From the positional distribution of 14C-labeled fatty acid and the change in the doubly labeled molecular species of phospholipids, it was concluded that tb degradation of dilinoleoylglycerophosphocholine and that of phosphatidylethanolamine could be accounted for by the action of phospholipase A1, while the degradation of dipalmitoylglycerophosphocholine proceeded through the action of phospholipase A2. Dimyristoylglycerophosphocholine was probably cleaved by the combined action of both phospholipases A1 and A2. Up to 10 mM tetracain, added to the chase medium, effectively blocked the action of both phospholipase activities. A considerable part of 2-linoleoyl- and 1-palmitoylglycerophosphocholine liberated during the chase was reutilized for phosphatidylcholine synthesis without further degradation.

Animals↗
PubMed1977

Aminoacyl adenylate, a normal intermediate or a dead end in aminoacylation of transfer ribonucleic acid.

The shape of the time curve for the aminoacylation of tRNA has been investigated using five different amino acid:tRNA ligases. Four of these enzymes showed a lag in the time curve during the early phase of the first catalytic turnover of the enzyme. In each case, the lag period could be abolished by preincubating the ligase with amino acid, ATP, and Mg2+ under conditions known to give an aminoacyl adenylate-enzyme complex. With all five ligases the steady state rate of transfer from the preformed aminoacyl-adenylate complex to tRNA was approximately the same as that of the overall reaction.

Adenosine Monophosphate↗
PubMed1977

Codon-acticodon recognition in the valine codon family.

An in vitro protein-synthesizing system completely dependent on added valine tRNA (valyl-tRNAval) and programmed with RNA from the phage MS2 has been used to investigate the incorporation into MS2 coat protein of valine from isoaccepting valyl-tRNAsval with the anticodons U AC (U represents 5-oxyacetic acid uridine monophosphate), GAC, and IAC in response to the four valine codons GUU, GUC, GUA, and GUG. By examining the incorporation of valine into NH2-terminal and internal positions of three tryptic peptides from the MS2 coat protein it has been established that these anticodons each recognize all four valine codons. We therefore conclude that under our conditions of in vitro protein synthesis the genetic code, as far as the valine codons are concerned, is operationally a two letter code, i.e. the third codon nucleotide has no absolute discriminating function.

Amino Acid Sequence↗
PubMed1976

Metabolism of different monoacylphospholipids in isolated hepatocytes and the intact rat.

The 1-[3H] palmitoyl, 2-[3H] oleoyl, and 2-[14C] linoleoyl derivatives of sn-glycero-3-phosphoethanolamine and the corresponding derivatives of sn-glycero-3-phosphocholine were injected intraportally to rats and their incorporation into liver lipids was studied 15 min thereafter. Both the uptake by the liver and the degree of acylation was higher for the unsaturated compounds. The uptake of lysophosphatidylethanolamine was higher than that of lysophosphatidlycholine. The metabolism of 1-lysophosphatidylethanolamine was also studied in isolated hepatocytes. The degree of hydrolysis was much more prominent than in vivo. After injecting 2-[14C] linoleoyl derivatives, a large part of the 14C was recovered in the dienoic phospholipids. Subfractionation by reversed-phase partition chromatography showed that the isotope was located in the palmitoyllinoleoyl and stearoyl-linoleoyl fraction. The 100 X stearoly/(palmitoyl + stearoyl) ratio was 84 in dienoic phosphatidylethanolamine and 59 in dienoic phosphatidylcholine. This preference for stearic acid is significantly larger than in other pathways yielding dienoic phospholipids. It can be concluded that the monoacylphospholipid acyltransferase reactions operating at positions 1 or 2 yield different saturated acyl chain profiles in phosphatidylethanolamine and phosphatidylcholine of a specific unsaturation. This may be important in the regulation of the fatty acid composition of the membrane phospholipids.

Animals↗
PubMed1976

Influence of chain length and unsaturation on the effects of fatty acids on phosphoglyceride biosynthesis in isolated rat and pig hepatocytes.

Hepatocytes isolated from rat or pig by collagenase perfusion were incubated with [3H]glcyerol and different albumin-bount fatty acids. Among C22 fatty acids docosahexaenoic acid stimulated phosphatidylethanolamine synthesis in rat hepatocytes most effectively. Addition of docosahexaenoic acid plus either palmitic or stearic acid resulted almost in the same stimulation whereas combinations of this acid with lauric or myristic acid had no effect. Lauric acid and myristic acid alone inhibited phosphatidylethanolamine synthesis. The chain length specificity for monoenoic fatty acids was similar, the hexadecenoic and octadecenoic acids (both cis and trans) being most stimulatory. The addition of 0.2 mM ethanolamine markedly stimulated phosphatidylethanolamine synthesis, but most effects of fatty acids were similar in its presence or absence.

Adipose Tissue↗
PubMed1975

Regulation of phospholipid biosynthesis in isolated rat hepatocytes. Effect of different substrates.

The effects of choline, ethanolamine and its N-methyl analogs, different fatty acids, and L-methionine on phospholipid biosynthesis via the CDP-ester pathways and the methylation pathway were studied in rat hepatocytes. Phosphatidylethanolamine synthesis was stimulated severalfold by 0.02 to 0.1 mM ethanolamine, especially in the presence of long chain unsaturated fatty acids. At higher concentrations of ethanolamine, phosphorylethanolamine accumulated but the level of CDP-ethanolamine and the rate of phosphatidylethanolamine synthesis did not increase further. The rate of phosphatidylcholine synthesis via the CDP-ester pathway responded in a way analogous to that of phosphatidylethanolamine synthesis upon the addition of choline and fatty acid, except that a 10- to 20-fold higher concentration of choline was required for maximal stimulation, probably due to the rapid oxidation of choline to betaine. Phospholipids containing N-monomethyl- or N,N-dimethylethanolamine were efficiently formed from the corresponding free bases in the absence of ethanolamine and choline. Ethanolamine, but not other bases, inhibited completely phospholipid formation from N-monomethylethanolamine, probably as a result of competition at the level of CDP-ester formation. The data indicate that the cytidylytransferase reactions are rate-limiting steps in the synthesis of phosphatidylethanolamine and probably also phosphatidylcholine. In addition, the availability of diacylglycerol and its fatty acid composition may significantly affect the rate of phospholipid synthesis. The rate of phosphatidylcholine formation via phospholipid N-methylation approximately doubled when L-methionine was added at concentrations similar to that in rat plasma. Under these conditions the rate of phosphatidylcholine synthesis via this pathway was 20 to 40 percent of that via diacylglycerols and CDP-choline. The methylation of phosphatidylethanolamine to phosphatidylcholine remained essentially constant when the rate of phosphatidylethanolamine synthesis was varied 8-fold, but was significantly reduced when the formation of N-monomethyl- or N,N-dimethylphospholipid was stimulated by addition of the corresponding base. These phospholipids not only replaced phosphatidylethanolamine as the substrate for methylation but also increased the rate of phosphatidylcholine formation via this pathway. A method for the determination of nanomole amounts of different ethanolamine compounds is described.

Animals↗