Intestinal brush border peptidases: activities in normal and abnormal peroral intestinal biopsy specimens

Discriminating substrates were used to develop assays that accurately measure the activity of each of four brush border peptidases in peroral jejunal biopsy specimens. Seventy-five biopsy specimens, 43 normal and 32 abnormal, were assayed for aminopeptidase A (EC 3.4.11.7), aminopeptidase N (EC 3.4.11.2), and disaccharidases, and 37 of these were assayed for membrane glycylleucine peptidase and Zn2+-stable aspartyllysine peptidase. Peptidase levels in normal biopsy specimens from males and females did not differ. Only aminopeptidase A levels changed significantly with age. The mean +/- SD units per gram of protein for each enzyme in peroral biopsy specimens of normal intestine were aminopeptidase A 1.7 +/- 0.7 for children and 3.1 +/- 1.3 for adults, membrane glycylleucine peptidase 16.3 +/- 10.6, aminopeptidase N 35.5 +/- 13.2, and Zn2+-stable aspartyllysine peptidase 42.6 +/- 28.5. In abnormal biopsy specimens, levels of three of the peptidases and the disaccharidases were significantly decreased, 37% to 51%. In contrast, aminopeptidase N activity was decreased only 7% in the abnormal biopsy specimens. These results provide a basis for further studies investigating the role of brush border peptidases in normal digestion and various pathologic states, including the search for individuals with brush border peptidase deficiencies.