Some studies on the biosynthesis of the molecular species of phosphatidylcholine from rat lung and phosphatidylcholine and phosphatidylethanolamine from rat liver

Abstract

SUMMARYr.Atdifferent timeintervals afterinjectionof [r(3)-SH]glycerol, theincorporation of glycerol into the various molecular species of phosphatidylcholine and phosphatidylethanolamine from rat liver, and phosphatidylcholine from rat lung was determined.2. The results indicate that, in liver, a de rtovo synthesis is primarily operating in the biosynthesis of linoleic acid-containing molecules of lecithin and of the hexaenoic molecular species of phosphatidylethanolamine. An acylation of monoacyl derivatives of these phospholipids is suggested to play an important role particularly in the formation of arachidonic acid containing molecular species of these phospholipids.3. In lung, the de MOVO synthesis was found to contribute also primarily to the linoleic acid-containing lecithins, though it also represents an important pathway for the synthesis of tetraenoic, monoenoic and, perhaps to a lesser extent, disaturated lecithins. A deacylation-reacylation mechanism may contribute significantly to the formation of dipalmitoyl lecithin, a major constituent of lung pulmonary surfactant.4. Acylation of I-palmitoyl-sn-glycero-3-phosphorylcholine with various labeled fatty acids or acyl-CoA esters was studied in the presence of microsomes from rat lung and liver. In the presence of microsomes from lung a significant uptake of palmitic acid was observed into the z-position of lecithin, this in strong contrast to the findings with liver microsomes where only a very limited uptake of palmitic acid was observed. The results endorse the findings from the in vivo studies that the acylation of monoacyl-sn-glycero-3-phosphorylcholine may play an important additional role in maintaining the high level of dipalmitoyl lecithin in lung.5. Comparison of the composition of phosphatidylethanolamine and lecithin from lung suggested, in support of previous observations by other investigators, that the methylation of phosphatidylethanolamine does not represent an important pathway for the formation of dipalmitoyl lecithin.

The effect of fasting and refeeding on the composition and synthesis of triacylglycerols, phosphatidylcholines, and phosphatidylethanolamines in rat liver

“…The livers were removed and homogenized in 0.33 M sucrose/O.01 M Tris (pH 7.4) with the aid of a Potter-Elvehjem homogenizer (1 g liver/IO ml). The microsomal and 105,OOOg supematant fractions were isolated from the liver homogenates as described previously (13). The microsomal pellets were resuspended in 0.125 M KCX0.1 M Tris (pH 7.4).…”

Phospholipase A2 in rat-lung microsomes: Substrate specificity towards endogenous phosphatidylcholines

“…No evidence was found for the existence of phospholipase A activity in lamellar bodies. 4. The microsomal phospholipase A, was more active towards phosphatidylcholines containing an unsaturated fatty acid at the 2-position than towards the disaturated phosphatidylcholines.…”

“…Both studies in vivo [4,5] and in vitro [6,7] have shown, however, that the principal ~hosphatidylcholines synthesized de novo are species which contain palmitic acid at the l-position and an unsaturated fatty acid at the S-position. Thus, the synthesis of dipalmitoylphosphatidylcholine must be the result of a mechanism which replaces the unsaturated fatty acid at the 2-position with palmitic acid.…”

Effects of vasopressin on the synthesis of phosphatidylethanolamines and phosphatidylcholines by isolated rat hepatocytes

“…There are several differences in the utilization of diacylglycerol by cholineand ethanolaminephosphotransferase [27,28], the latter one showing a preference for highly unsaturated species. It is very well possible that the newly formed diacylglycerol is a better substrate for ethanolaminephosphotransferase, which would explain the increase in the incorporation of ethanolamine into phosphatidylethanolamines.…”