Biosynthesis of Phosphoglycerides and Neutral Glycerides in Rabbit Lung

Biosynthesis pathway of phosphoglycerides and neutral glycerides in the lung was studied in this paper. Especially, the time course of incorporation of 14C-glycerol into triglyceride (TG), diglyceride (DG), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidic acid (PA) and glycerophosphate (GP) were studied in order to make clear the pathway of biosynthesis of these lipids in the lung, and they were compared to the liver. The following observations were made: 1) the amount of 14C-glycerol that was incorporated into hole lipids of the lung slices for 120 minutes was about 1/3 of that of the liver slices. 2) In the liver slices, TG synthesis was the most. In the lung slices, on the other hand, PC synthesis was the most but TG synthesis was very low. The biosynthesis of PC of the lung slices was equal to, or might be slightly excellent to that of the liver slices in the same wet weight. 3) The time course of incoporation of the isotope into DG of the lung slices suggested strongly that DG was a direct precursor of TG, PE and PC. But it seemed that PA might not be a precursor of these glycerides in the lung slices, according to it's time cuorse. 4) From the point of the time cuorse of incorporation of the isotope into PA in the lung homogenates, it became to be almost sure that PA was a precursor of TG, PE and PC. The time cuorse of radioactivity of glycerol, GP and PA, and the relation of the each time cuorse strongly suggested that there was a pathway as follows: glycerol → glycerophosphate → phosphatidic acid. 5) These findings suggest that the pathway of de novo synthesis of lipids in the lung is as follows: glycerol → glycerophosphate → phosphatidic acid → diglycerid → triglycerid and phosphoglycerides. Namely, it becomes sure that phosphoglycerides and neutral glycerides of the lung are producted through Kornberg's pathway and Kennedy's pathway as same as the liver