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Biomedical subjects

B Akesson

Publications and source records attributed to B Akesson.

At least 127 records · Page 7Linked to original sources
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↗
PubMed1975

Work in progress. Occurence of phospholipase A1 and A2 in human decidua.

Phospholipase A2, an enzyme which may regulate the formation of polyunsaturated fatty acids utilized for prostaglandin synthesis, was found to have significant higher activity in decidual than in myometrial tissue. The major part of phospholipase A2 in the decidua had an acid pH optimum, which indicates that most of the enzyme is stored in the lysosomes of this tissue. These findings, together with previous observations, lend further support to the view that lysosomal phospholipase A2 released within decidual cells might be a trigger of abortion and parturition.

Buffers↗
PubMed1975

Biosynthesis of phosphatidylethanolamines and phosphatidylcholines from ethanolamine and choline in rat liver.

1. The kinetics of phosphatidylcholine and phosphatidylethanolamine synthesis in rat liver were followed 5-60 min after the intraportal injection of [14-C]choline and [3-H]-ethanolamine. 2. At all time-intervals the specific radioactivity of CDP-choline was only about half that of phosphorylcholine. This indicated that CDP-choline was formed at a similar rate from phosphorylcholine and phosphatidylcholines, the latter probably through the reverse reaction of cholinephosphotransferase (EC 2.7.8.2.). In view of recent data obtained from experiments in vitro this implies a significant role for the cholinephosphotransferase reaction in the turnover of molecular species of phosphatidylcholine. 3. The specific radioactivity of CDP-ethanolamine was about twice that of phosphorylethanolamine at all time-intervals studied. This supports a previous suggestion that the liver phosphorylethanolamine pool is subject to compartmentation and shows that there is no rapid equilibration between different pools. In contrast with a recent study, no evidence was found for any significant methylation of phosphoryl-or CDP-ethanolamine to the corresponding choline derivative. 4. Quantitative data on the biosynthesis of molecular species of phosphoLIPIDS via CDP derivatives were calculated according to simple kinetic models. They were in the same range as those calculated from earlier data on precusors incorporated via diacylglycerols. 5. The proportion of radioactive phosphatidylethanolamines appearing in the plasma was approximately ten times lower than that for phosphatidylcholines. No selectivity was observed in the transfer into plasma of different molecular species of phosphatidylethanolamine.

Animals↗