Search

Summary Lung Type II epithelial cells contain lamellar bodies, the storage form of surfactant, which is predominately dipalmitoyl-phosphatidylcholine. Isolated lamellar bodies, free of microsomal and mitochondrial contamination have significant phosphatidic acid phosphohydrolase activity. Calculations based on enzyme distribution indicate that as much as 40% of the phosphatidic acid phosphohydrolase activity within the Type II cell is associated with the lamellar bodies. This high concentration of phosphatidic acid phosphohydrolase, a key enzyme in phospholipid biosynthesis, suggests that the phosphatidylcholine stored within the lamellar bodies may be synthesized at the perilamellar surface.

Lipids were labeled with (33)P during frost hardening of two varieties of winter wheat (Triticum aestivum), hardy Kharkov and much less hardy Champlein. The main labeled compounds were phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidylglycerol. With time of incorporation the proportion of the radioactivity incorporated into the lipids increased in phosphatidylcholine, especially in Kharkov and at 1 C. During hardening, phospholipid synthesis was greatly stimulated in Kharkov, but much less in Champlein. The proportion of the phospholipids synthesized changed only little with hardening, with a trend towards an increase in phosphatidylcholine. Increased phospholipid synthesis does not seem to be a prerequisite to hardening in winter wheat. However, a high rate of phospholipid synthesis may be required to maintain frost resistance.

FATrY ACID BIOSYNTHESIS. . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 288 Acetyl-CoA Synthetase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 289 Acetyl-CoA Carboxylase , ., .... .. 289 De novo System of Fatty Acid Biosynthesis.... .. . .... 289 Elongation Systems of Fatty Acid Biosynthesis. . . . . . . . . . . . . . . . . . . . . . .. 290 Monounsaturated Fatty Acids . .... .. . 290 Polyunsaturated Fatty Acids ........ , 292 FATrY ACID CATABOLISM • • • • • • • • . • • • • • • • . • • . . • • • • • • • • • • • ' " • • • • • • • • • . • , • • • 294 PHOSPHOLIPID BIOSyNTHESiS • • • • . • . • • . . • . • • • . . . • . • • • • • • • ' • . • • • • . • • • • • • • • • • • • 297 Phosphatidic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . " 297 Phosphatidylglycerol, Diphosphatidylglycerol. . . . . . . . . . . . . . . . . . . . . . . . .. 299 Phosphatidylserine, Phosphatidylethanolamine, Phosphatidylcholine. . . . . .. 299 PHOSPHOLIPASES. • • • . . . . . . . . . . . . • . . . • . . • • . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . .. 300 GLYCOLIPID METABOLISM. • • • . . . . . . . . . . . . . . • . . • . . . . . . . • . . . . . . . . . . . . . . . • . • . . 301 PROGRAMMATION OF LIPID SyNTHESIS. • . . . . . • • • . • • . . . . . . . . . . • . . . . . . . . . . . . . . .. 302 LIPID SYNTHESIS DURING AGING. • • • • • • • . • . • • • • . . • • • • • . • . • • • • • • • • . . . . • . . • • • . 303 LIPID TRANSFERS IN VITRO. . • . . . . . . . . . . . . . • . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . .. 304 MEMBRANE LIPID TURNOVER. . • • . . . . . . . . . • . . . • . . . . . . . . . . . . . . . . . . . . . . . . . • . . .. 304

Fourty-eight-hour starved albino rats were fed C14-labelled fatty acids, glycerol and lecithin and serum assays were carried out three hours afterwards for specific radioactivities of phospholipids and their individual fatty acid constituents, with the results which may be summarized as follows:1. Phospholipid biosynthesis in the intestinal wall from dietary fatty acids was prominently active when the animals were fed linoleic acid.2. The results obtained indicate that the two-fatty-acid constituents of phospholipid synthetized in the intestinal wall of animals receiving linoleic acid are probably both linoleic acids.3. It is likely that neither dietary glycerol nor the glycerol of dietary lecithin takes part in the intramural phospholipid biosynthesis.

Thyrotropin stimulates the incorporation of 32P into phospholipids of thyroid slices incubated with 32PO4. To determine whether this effect could be secondary merely to an increase in the specific activity of the terminal (γ) P of ATP, a precursor of phospholipid P, the effect of thyrotropin on calf thyroid slice ATP was measured with an assay which is selective for ATP-γ-32P specific activity. Thyrotropin increases the specific activity of lipid 32P uniformly without altering that of ATP-γ-32P, indicating that it exerts its effect at a step beyond ATP in the sequence of phospholipid biosynthesis. There was no significant effect of thyrotropin on the ATP content of thyroid slices.

The presented data suggest that PAPase may, indeed, be important in the biosynthesis of lung phospholipids. The observed increase in the specific activity of rabbit lung precedes the "surge" of phosphatidylcholine concentration and surfactant biosynthesis by at least 24 hours. In human amnionic fluid, PAPase specific activity was markedly increased in pregnancies of 35 weeks of gestation or more. The increase in the specific activity of PAPase preceded the "surge" of acetone precipitated phosphatidylcholine. The reported studies may provide an additional procedure to examine the problems associated with surfactant biosynthesis.

Summary Microsomal preparations from rat liver catalyze the formation of 2-acyl-1,2-alkanediolphosphorylcholine from a long-chain 2-acyl-1,2-alkanediol and CDP-choline in the presence of Mg ++ or Mn ++ . The reaction is inhibited by Ca ++ . The results indicate that 2-acyl-1,2-alkanediol can substitute for 1,2-diglyceride in phospholipid biosynthesis.

Apres administration de phenobarbital chez le rat le renouvellement des phospholipides microsomiaux etudies par double marquage14C-32P n'est pas augmente alors que celui des phospholipides plasmatiques est ralenti. L'hypertrophie des membranes endoplasmiques n'est pas le resultat d'une augmentation de leur biosynthese et semble etre la consequence d'un ralentissement du catabolisme.

The larval fat body of Sarcophaga bullata was shown to be an effective system for the study of phosphatidylcholine biosynthesis. 32 P-phosphorylcholine was incorporated to the extent of 4·7 per cent in 1 hr at 30°C. This substrate was a precursor of phosphatidylcholine.