Localization of the monoglyceride pathway in subcellular fractions of rat intestinal mucosa

Abstract

The localization of the monoglyceride pathway in subcellular fractions of rat intestinal mucosa has been studied. The 2-octadecyl-(1- 14C)-glyceryl ether was used as a model substrate to replace 2-monoglyceride in the in vitro systems. The ability of brush border membranes and microsomal fraction to synthesize higher glycerides, particularly triglyceride, was compared. The results show that the total activity and the specific activity of diglyceride transacylase were higher in brush border membranes than in microsomal membranes. The purity of the brush border and microsomal membranes was monitored by biochemical “marker substances.” Microsomal contamination in the brush border fraction could not account for triglyceride synthesis attributed to the brush border. Brush border contamination in the microsomal fraction could account for from 30–100% of the triglyceride synthesis attributed to the microsomal fraction. However, brush border contamination in the microsomal fraction could not explain the high level of diglyceride synthesis attributed to the microsomal fraction. A determination of the structure of the intermediate diglyceride synthesized in the brush border and microsomal fractions showed that 1,2-diglyceride is made at both sites. The distribution of radioactivity of the original glyceryl ether substrate in subcellular fractions isolated from incubated homogenates of rat mucosa was determined. The brush border fraction contained the highest percentage of total radioactivity.