The course of digestion of different food proteins in the rat. Fractionation of the nitrogen in intestinal contents

I. The course of digestion of casein, a-protein (an isolated soya-bean protein) and of raw and heated soya-bean meal in the rat was examined and compared by analysis of the stomach and small intestine contents I , 2, 3 and 4 h after giving test meals of the different proteins.2. After centrifugation, the soluble nitrogenous compounds of the intestinal contents were separated by filtration on Sephadex gel G-25 into protein, peptide and amino acid fractions.3. The rates of stomach emptying varied widely; they were faster with a-protein than with casein, and both these proteins left the stomach more quickly than did the two soya-bean meals.4. The intestinal contents of rats given raw soya-bean meal contained considerably larger amounts of insoluble N and dry matter than did those of rats given the heated soya-bean meal;these, in turn, contained considerably more than did those of rats given casein or a-protein. 5.The intestinal contents of rats given a-protein or raw soya-bean meal contained considerably larger amounts of soluble N than did those of rats given casein or the heated soyabean meal.6. Fractionation in Sephadex G-25 of the soluble N of the intestinal contents of the rats given casein showed reduction with time in the amount of proteins, peptides and amino acids but the amounts of all these compounds were considerably less than in the corresponding fractions from the gut contents of the rats given a-protein, which was digested much more slowly.7. Similar fractionations of intestinal contents of rats given raw soya-bean meal showed an unchanging and very high content of undigested protein, probably of endogenous origin, and only small amounts of the peptide and amino acid fractions, whereas after giving the heated meal the initially large protein fraction progressively decreased.