Enantiomeric Diglycerides as Stereospecific Probes in Triglyceride Synthesis In Vitro

The stereospecificity of diglyceride acyltransferase (EC 2.3.1.20) was studied in the microsomes of rat intestine and liver using enantiomeric diglycerides as acceptors of labeled fatty acids. The diglyceride mixtures were prepared by combining equal amounts of synthetic 1,2- and 2,3-diglycerides of different degrees of unsaturation. The labeled triglycerides formed were resolved by argentation thin-layer chromatography, whereupon the products from each enantiomeric diglyceride moved to a different spot on the thin-layer plate.It was shown that both 1,2- and 2,3-diglycerides were utilized for direct acylation to triglycerides by both tissues. The diglyceride acyltransferase, if a single enzyme, showed a definite preference for the acylation of the 1,2-diglycerides. The intestine esterified more of the 2,3-isomer than did the liver. The yields of triglyceride depended upon the nature of the fatty acids involved, and their positional distribution on the glycerol molecule. The new method of stereospecific assessment of triglyceride biosynthesis in vitro is applicable to preparations of other subcellular fractions and to other suitable combinations of fatty acid and diglyceride precursors.