Studies on human intestinal proteolysis

Nitrogen losses from the human small bowel: obligatory losses and the effect of physical form of food

The amount and form of nitrogen lost from the human small intestine and the dietary factors which influence it have been studied in six ileostomists. Over a six day period the subjects were fed a series of diets including low nitrogen (LND) 0.17 g N/day, LND + soya beans (5.87 g N/day) and a high fibre diet (HFD) (10.6 g N/day). The soya beans were fed either whole or pureed to test the effect of physical form of food. Total N, protein, amino acids, urea, and ammonia were measured in ileostomy effluent which was collected throughout the study. Total N excretion was LND 0.91 (0.04) (SE) g/day; LND + whole soya beans (WSB) 2.26 (0.15) g/day; LND + pureed soya beans (PSB) 1.42 (0.12) g/day (WSB v PSB, p less than 0.001); and HFD 2.17 (0.11) g/day (HFD v PSB, p less than 0.001, HFD v WSB, NS). N losses as urea, ammonia, and free amino acids were less than 10-15% of total N, the remainder being protein (48-51%) and (by difference) peptides (20-30%). Eighty to 85% of effluent N was in the insoluble (pellet) fraction except on the low N diet where it was 66%. The physical form of food clearly influenced N digestibility in the soya beans whilst changes in dietary fibre seem not to have a significant effect.

Immunochemical quanitation of pancreatic endopeptidases in the intestinal contents of germfree and conventional rats

Two electrophoretically distinct trypsins and chymotrypsins and an elastolytic enzyme were isolated from rat pancreatic juice. Rabbit antisera against these enzymes were produced, and with an immunochemical technique the trypsins, chymotrypsins, and elastase were studied in the intestinal contents of conventional and germfree rats. In both types of rat the anionic trypsin and chymotrypsin were the most abundant and found in higher concentrations in the distal than in the proximal small intestine. The cecal and fecal concentrations of anionic trypsin were markedly higher in the germfree rat when compared to the conventional rat. Cymotrypsin was undetectable in the large intestine of either the conventional or germfree rat when this technique was used. Immunoreactive elastase was found in greater amounts in the distal small intestine, and high concentrations were demonstrated in the cecal contents and feces of the germfree rat. In contrast, no immunoreactive elastase was detected in the large intestine of the conventional rat. Gel filtration indicated that the immunoreactive anionic trypsin and elastase found in fecal extracts were of about the same molecular size as the native enzymes. The findings suggest that the intestinal microflora is instrumental in the inactivation and degradation of pancreatic trypsin and elastase but not chymotrypsin.

Functional, chemical, and clinical aspects of proteolytic enzymes in the alimentary canal

Knowledge of the structure and catalytic function of the pancreatic proteases has increased rapidly in recent years. These advances have been less spectacular in the case of pepsin, and information concerning mucosal enzymes of the small intestine and colon has not even reached the point where one can be certain of their number, far less their nature. The role of these enzymes in disease processes is probably not significant so far as the alimentary tract is concerned, and it is not even certain that the pancreatic proteases influence the course of acute pancreatitis -- they are of more interest to the clinician as diagnostic aids. Since undesirable consequences result from their deficient output, future research should be directed towards improving replacement therapy.