An examination of the stereochemical course of acylation of 2-monoacylglycerols by rat intestinal villus cells using [2H3]palmitic acid.

The stereochemical course of acylation of 2-monoacylglycerols by rat intestinal mucosa was investigated using isolated villus cells with 2-lauroylglycerol and [2H3]palmitic acid as substrates. The newly synthesized X-1,2-diacylglycerols and triacylglycerols were recognized on the basis of the content, positional distribution and molecular association of the fatty acids by gas-liquid chromatography/mass spectrometry in combination with sterospecific analysis. It was found that the free X-1,2-[2H3]palmitoyllauroylglycerols contained 74% sn-1,2- and 26% sn-2,3-enantiomers, which were utilized for triacylglycerol formation in the same proportion. Some of the 2-monolauroylglycerol became hydrolyzed and the released lauric acid was utilized along with [2H3]palmitic acid for diacylglycerol and triacylglycerol formation via both the phosphatidic acid and the 2-monoacylglycerol pathway. The contribution of the phosphatidic acid pathway (12-16%) was determined by estimating the relative proportion of the newly synthesized triacylglycerols containing [2H3]palmitic acid in the sn-2 position. After correcting for the contribution of the phosphatidic acid pathway, the sn-1,2-/sn-2,3-enantiomer ratio in the X-1,2-[2H3]palmitoyllauroylglycerol was estimated to be 71/29. These results are consistent with those previously obtained with glycerol-labelled 2-monoacylglycerols and intact tissue or homogenates of rat intestinal mucosa. It is suggested that the 2-mono-acylglycerol transacylase, if a single enzyme, possesses a low stereospecificity, or that two enzymes exist of unequal concentration and/or activity.