A BST RA CT Peptide hydrolases, catalyzing the hydrolysis of 13 dipeptides and 5 tripeptides into their respective amino acids, were studied in small intestinal mucosa and other tissues, in man and in the rat.Studies on the subcellular distribution of these enzymes showed enzyme activities in both the soluble and brush border fractions of the rat small intestinal mucosa, the former constituting 80-90% and the latter 10-15% of the total activity. Zymogram studies of peptide hydrolases, in both fractions, yielded multiple bands indicating multiple zones of enzyme activity. With most substrates a rather broad range of enzyme activities was observed in the soluble fraction differing only slightly from substrate to substrate, the exception being when L-leucyl-L-proline was used: this latter led to a zymogram pattern which was quite distinct. The synthetic substrates, L-leucyl-P-naphthylamide and Lleucinamide appeared to be hydrolyzed by two electrophoretically distinct enzymes, different from those hydrolyzing other leucyl-containing peptide substrates.Zymogram patterns of the brush border membrane fraction were quite different from those of the soluble fraction of rat small intestine indicating that enzymes from the two sources may be different. No comparable human data were obtained.Peptide hydrolases in the soluble fractions of various organs from the same species gave similar zymogram patterns, while those from the plasma membrane-bound fractions of different organs in the same species were peculiar to each organ. From these data, it is suggested that peptide hydrolases in the brush border and the soluble fractions of small intestine are distinct enzymes and may play different roles in cellular function.
Groups of rats were fed isocaloric amounts of diets rich in starch, protein, or fat. After 7 days, activities of sucrase, maltase, lactase, alkaline phosphatase, L-phenylalanylglycine hydrolase, and L-leucyl-L-alanyl hydrolase were measured in the duodenal, jejunal, and ileal mucosa of fed rats. Peptide hydrolase and alkaline phosphatase activities were significantly higher in rats fed high-protein diets, particularly in the ileum. Disaccharidases were highest in rats fed high-starch diets, especially in jejunum; the lowest activities of peptide hydrolase were seen with this diet. The high-fat diet was generally associated with intermediate activities of most enzymes, except disaccharidases, which were lowest on this diet. The different macromolecular nutrients were associated with adaptive differences in intestinal enzyme activities, which were biologically appropriate and coordinated with similar known changes in pancreatic and other enzyme activities concerned with assimilation of the particular food. However, other less interpretable changes occurred, which may have been due to effects on pancreatic secretion or on the metabolism, growth, and differentiation of intestinal cells.
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