240 Kinetics of Trypsin Digestion

The anomalies of enzyme action have frequently been accounted for by the assumption of an intermediate compound between the enzyme and the substrate. I t was shown, however, by Nelson and Hitchcock t that in the case of invertase the experiments could not be accurately calculated on this basis. The writer found with trypsin' that although the effect of varying the substrate concentration could be accounted for, the effect of varying both the substrate and inhibiting substances could not, provided the law of mass action was assumed to hold. The question is one of such importance from the view of all enzyme reactions, however, that it seems important to obtain direct experimental evidence in regard to the existence of such a compound. The statement is frequently made that the substrate protects the enzyme from heat inactivation and this has been considered as evidence for the existence of a compound between the substrate and enzyme. I t has been found, 3 however, that this protective action does not become manifest at once but only after the enzyme and substrate have been in contact, when it becomes more and more pronounced. I t can further be shown that the products of digestion afford very marked protection and that this effect is apparent at once. I t appears probable, therefore, that the protective action of the substrate solution is not due to the substrate itself but to the products formed by the action of the enzyme and that this is the reason for the delay in the protective action.