STRUCTURAL STUDIES OF NEUTRAL GLYCERIDES AND PHOSPHOGLYCERIDES OF RAT LIVER

The distribution of fatty acids esterified at each position of glycerol in triglycerides (TG), phosphatidyl choline (PC), and phosphatidyl ethanolamine (PE) of rat liver was determined. The carbon number distribution of TG and diglyceride acetates derived from PC and PE was also determined. Each of the TG positions showed a distinct distribution of fatty acids that was not arranged randomly, indicating pairing of some acids. The composition of the fatty acids esterified at the 1-position of PC and PE was the same, but differed from the 1-position of TG; the 2-position differed in all three classes. The carbon number distribution of PC diglyceride acetates was different from that of PE diglyceride acetates and neither agreed with the random distribution values calculated from the experimentally determined compositions of the 1- and 2-positions of each class, indicating preferential pairing of some acids in these lipid classes also. Selectivity of diglycerides used for the biosynthesis of either TG or phospholipids or both is substantiated by the lack of agreement between the TG carbon number distribution determined experimentally and the distribution calculated from values of either PC or PE diglyceride acetates plus the values of the 3-position of the TG. These findings for rat liver are the opposite of those reported in a companion paper in which tumor cells did not show selectivity of diglycerides used for TG and PC biosynthesis. © 1969.