Studies on Human Intestinal Proteolysis

Abstract

The enzymic digestion of protein to acid-soluble peptides has been measured in the ileal drainage material from human subjects in whom an ileostomy was established for the treatment of ulcerative colitis or polyposis coli. This activity (TPA) is sensitive to dietary protein but insensitive to fat and carbohydrate, and follows a diurnal rhythm with increased enzyme output during the night. Two-thirds of this proteolytic activity is due to the pancreactic enzymes trypsin and chymotrypsin. Experiments with neomycin sulphate suggest that not more than 7 per cent is due to bacterial enzymes. No contribution appeared to be made by small intestinal epithelium, and it is considered that the remainder of this activity can be ascribed to other pancreatic enzymes. The faecal output of TPA in two subjects before operation was considerably less than that from their ileostomy when this was later established. Reasons are presented for believing the human small intestine capable of digesting several kg of protein daily. While it is suggested that protein digestion may continue unimpaired even in the presence of severe pancreatic dysfunction, estimation of TPA on homogenates of ileal or duodenal material is a convenient procedure which is likely to give more useful information about pancreatic function than the estimation of a single specific enzyme.

Key-words:

• Intestine, small
• peptides
• digestion
• enzyme tests
• absorption