LONGITUDINAL-STUDY OF THE HUMAN INTESTINAL BRUSH-BORDER MEMBRANE-PROTEINS - DISTRIBUTION OF THE MAIN DISACCHARIDASES AND PEPTIDASES

Abstract

The longitudinal distribution of the main brush border membrane hydrolases was studied in 6 entire human small intestines, one of which was found to be lactase-deficient. Sucrase and lactase activities were highest in the jejunum, whereas glucoamylase activity rose steadily and reached its highest activity near the ileocecal valve. Maltase activity distribution was intermediate between that of sucrase and of glucoamylase. Neutral aminopeptidase, acid aminopeptidase and dipeptidyl peptidase IV activities tended to increase toward the end of the small bowel, the latter 2 activities rising more than the first one. Furthermore, the protein compositions of the brush border membrane in the jejunum and in the ileum were compared after electrophoresis on polyacrylamide gels and crossed-immunoelectrophoresis; protein patterns were similar along the gut, and enzyme-specific activities varied in parallel with the amounts of their corresponding proteins. In the lactase-deficient intestine, the protein band corresponding to lactase was not visible. Maximal digestive capacity was thus localized in the jejunum only for disaccharides, and in the ileum for the more complex substrates, oligosaccharides and peptides; this finding suggests that the ileum may play a greater role in their terminal digestion than is usually admitted.