The products of proteolysis of some purified proteins.

Recent studies on the digestion of proteins by the proteolytic enzymes of the gastrointestinal tract have resulted in a considerable revision of our concepts on how these enzymes act. Tiselius and Eriksson-Quensel (1) studied the mechanism of the peptic digestion of crystalline egg albumin by electrophoretic examination of the products of proteolysis. They observed that, as digestion proceeded, the average size of the peptides formed remained constant. From these results, they postulated that each protein molecule is rapidly degraded to its ultimate products without the intervening production of larger units. They have called this an “all or none” mechanism of proteolysis. Haugaard and Roberts (2) reached similar conclusions from experiments on the digestion of @-lactoglobulin by crystalline pepsin. They reported that during digestion the increase in terminal amino nitrogen (determined by the nitrous acid manometric technique of Van Slyke (3)) increased lineally with the total non-protein nitrogen. A similar study was made by Winnick (4) on the digestion of casein by chymotrypsin, trypsin, pepsin, ficin, and papain. His data were consistent with those of the above workers. We have extended these observations in the present, paper, employing for our studies trypsin acting on crystalline bovine serum albumin and purified r-globulin, and pepsin on crystalline bovine serum albumin, purified bovine fibrin, and twice recrystallized egg albumin. The resu1t.s to be presented also favor a rapid or immediate degradation of the protein molecules to peptides of characteristic size, with the liberation of little or no free amino acid nitrogen.