Phosphatidyldimethylethanolamine Research Articles

Biochemical development of surface activity in mammalian lung. 3. Structural changes in lung lecithin during development of the rabbit fetus and newborn.

Extract: This is a report of studies with gas-liquid chromatography of the fatty acids on the α- and β-carbons of surfae active and nonsurface active lecithins isolated from alveolar wash and from residual lung after wash in the developing rabbit fetus. The total fatty acids of lecithin show no clear tendency toward greater saturation with development. In alveolar wash, there was greater saturation of fatty acids (65%) compared with total lung (57%). Fatty acids separately determined on α- and β-carbons of lecithins showed significant developmental differences. Differnces in surface active acetone-precipitated lecithin and nonsurface active acetone-precipitated and acetone-soluble lecithin were in the β-carbon fatty acids. They were highly saturated (+70%) in surface active lecithin but only about 25% saturated in monsurface active lecithin. Concentration of acetone-precipitable lecithin in whole lung rises during fetal development to a peak (84%) with breathing. There was a marked increase in acetone-precipitable lecithin in alvcolar wash after 1 h of breathing (0.35 mg/g dry weight lung in nonbreathing full term to 9.8 mg/g), a 30-fold increase. During gestation, both α- and β-component palmitic acid (C16:0) rose abruptly after day 29 (α-45 to 67% and β-48 to 60%) when alveolar lecithin becomes surface active. The greatest increase in α- and β-palmetic acid followed the onset of breathing, and by day 2 of age, α-palmitic 85%, β-palmitic 62.5%. Thus, dipalmitoyl lecithin is the greatest single identifiable fraction of surface active lecithin isolated from rabbit alveolar wash. Acetone-soluble lecithins, even in the breathing animal, have only about 25% palmitic acid on the β-carbon. Early 29-day fetus, deliverd by cesarean section, synthesized de novo 100% of his surface active lecithin (CDP-choline +α –β-diglyceride pathway), predominantly α- and β-palmitic acid (69.7 and 61.2%, respectively). Phosphatidyl dimethylethanolamine (PDME), a surface active intermediate in the trimethylation of phosphatidyl ethanolamine (PE) to form lecithin, showed largely an α-palmitic/β-myristic acid (53/60%) distribution. Since the rate-limiting reaction is the first methyl group in PE, PDME represents the lecithin end product, another pulmonary surface active lecithin with α-palmitic/β-myristic acids. Speculation: Use of the β-carbon fatty acids as markers in studying the acetone-precipitated surface active fraction of lecithin isolated from alveolar wash will permit an assessment of the contributin of each of the two major pathways in the biosynthesis of surface active lecithin.

Phospholipid metabolism in Ferrobacillus ferrooxidans.

The lipid composition of the chemoautotroph Ferrobacillus ferrooxidans has been examined. Fatty acids represent 2% of the dry weight of the cells and 86% of the total are extractable with organic solvents. About 25% of the total fatty acids are associated with diacyl phospholipids. Polar carotenoids, the benzoquinone coenzyme Q-8, and most of the fatty acids are present in the neutral lipids. The phospholipids have been identified as phosphatidyl monomethylethanolamine (42%), phosphatidyl glycerol (23%), phosphatidyl ethanolamine (20%), cardiolipin (13%), phosphatidyl choline (1.5%), and phosphatidyl dimethylethanolamine (1%) by chromatography of the diacyl lipids, by chromatography in four systems of the glycerol phosphate esters derived from the lipids by mild alkaline methanolysis, and by chromatographic identification of the products of acid hydrolysis of the esters. No trace of phosphatidylserine (PS), glycerolphosphorylserine, or serine could be detected in the lipid extract or in derivatives of that extract. This casts some doubt on the postulated involvement of PS in iron metabolism. After growth in the presence of (14)C and (32)P, there was essentially no difference in the turnover of either isotope in the glycerolphosphate ester derived from each lipid in cells grown at pH 1.5 or 3.5.

The incorporation of palmitate-1-14C by rat lung in vitro.

The incorporation of palmitate-1-14C into various lipid fractions was studied in rat lung in vitro. Most of the radioactivity was found in phospholipid, although in terms of decreasing specific activity the lipids were ranked: free fatty acid (FFA), glycerides, phospholipid. In addition to the usual glycerophosphatides, rat lung contained a substance with some of the chromatographic characteristics of phosphatidyl dimethylethanolamine. In terms of decreasing specific activities the phospholipids were ranked: phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl dimethylethanolamine, phosphatidyl serine plus phosphatidyl inositol, sphingomyelin plus lysophosphatidyl choline. Inhibition of oxidative energy production by hypoxia, cyanide, or low temperature markedly depressed the esterification of palmitate-1-14C. Less marked depression was observed in the absence of exogenous glucose. In all cases the decreased incorporation was associated with an increase in the total and specific radioactivity in tissue FFA. It is concluded that energy-independent exchange reactions are probably of little importance in the incorporation of FFA into esterified lipids of lung tissue. Under conditions of metabolic inhibition the penetration of labelled FFA into the tissue FFA pool does not appear to limit esterification.

The biochemical development of surface activity in mammalian lung. I. The surface-active phospholipids; the separation and distribution of surface-active lecithin in the lung of the developing rabbit fetus.

Extract: A simple technique, precipitation with acetone, was described to separate the surface-active lecithin fraction from the nonsurface-active fraction. Surface activity in lung phospholipids was found in the acetone-precipitated fractions of lecithin, sphingomyelin, phosphatidyl dimethylethanolamine and phosphatidyl inositol. Normal surface activity of saline extract of pooled fetal rabbit lung was observed from 28 days of gestation. It was possible to isolate surface-active lecithin from lung parenchyma long before the 29th day of gestation when surface-active lecithin first is found in the alveolar wash. During the nonbreathing fetal state, even at term, only 11% of lecithin from alveolar wash is surface-active increasing after one hour's breathing to approximately 50% of the total lecithin. The rabbits delivered prematurely after 28 full days of gestation clinically had respiratory distress and their percentage of surface-active lecithin in alveolar wash increased at a slow rate compared to full-term animals. Good temporal correlation was seen between intracellular storage of surface-active lecithin during the fetal state and the findings with electron microscopy of increasing numbers of osmiophilic inclusion bodies as gestation progresses. Speculation: Surface activity is shared by several phospholipids in lung but is related principally to lecithin. During fetal development there is production of intracellular surface-active lecithin with storage possibly in osmiophilic lamellar inclusion bodies until near term when some (11%) begins to appear in alveolar wash. After breathing, a great release of surface-active lecithin into alveolar wash occurs, with 50% of alveolar lecithin being surface active throughout the life of the animal. Prematurely delivered rabbits take much longer to increase their surface-active alveolar lecithin.

Lecithin formation by methylation of intact phosphatidyl dimethylethanolamine

S>Results are reported from tracer studies of lecithin formation by methylation of intact phosphatidyl dimethylethanolamine (DME). After incubation of C/sup 14/ labeled DME with rat liver slices, the isotope was found to be present in the DME as well as in the choline moiety of the phospholipids. Results are tabulated from typical experiments. Possible reaction mechanisms involved are discussed. (C.H.)