Nature of the Anti-tryptic Action of Serum 49 



particular substance which causes the inhibition, existing 1 at 

 present, left this question entirely unsettled. 



The first point considered was the fate of trypsin in mixtures 

 with serum. Several effects seemed possible; (1) that trypsin 

 was destroyed by the serum and that the action was purely toxic ; 

 (2) that the reaction between trypsin and serum was one of 

 physical adsorption; and (3) that the reaction might be of a 

 chemical nature. 



In some previous work reported before this society 1 , it was 

 found that trypsin could be easily isolated from fresh and com- 

 mercial extracts of the pancreas in a state of great purity by 

 means of colloidal iron. It seemed possible, therefore, that this 

 method of isolating the ferment might prove of service in study- 

 ing the problem in hand; and indeed such was the case. 



By means of adequately chosen experiments it was found that 

 trypsin could be recovered quantitatively from mixtures with 

 serum even after prolonged periods of incubation. Other means 

 of isolating trypsin were also found, for example, by treating 

 mixtures of trypsin and serum with adequate amounts of ethyl 

 alcohol, in which case the proteins of the serum are precipitated 

 and the trypsin remains in solution. It might be added that the 

 latter method is not quantitative. 



These experiments indicate, I believe, the following; that the 

 anti-tryptic action of serum is not due to a destruction of the 

 ferment by the serum, but that the inhibitory action of serum is 

 either due to an adsorption of the trypsin by the serum, or that 

 the reaction is a chemical one, of a reversible nature. 



When mixtures of trypsin and a digestible substrate such as 

 casein are treated with alcohol, after a brief incubation, some of 

 the trypsin can be recovered. After digestion of the casein is 

 completed none of the trypsin can be recovered. When such 

 mixtures are treated with colloidal iron the trypsin can not be 

 isolated by reason of the fact that the reaction takes place be- 

 tween the casein and the iron, forming casein-ferrate. When, 

 however, serum is first added to a mixture of trypsin and casein, 

 in sufficient amount to cause inhibition of digestion, and this is 

 then treated with colloidal iron, both the serum proteins and the 

 casein are precipitated and the trypsin remains in solution. The 



1 Epstein, Albert A., Proc. Soc. Exper. Biol, and Med., 1921, xix, 3. 



