FURTHER OBSERVATIONS ON THE DIGESTION 

 OF FIBRIN AND CASEINOGEN BY TRYPSIN 



By EDWARD STAFFORD EDIE. 



From the Physiology Department, Aberdeen University. 



{Received June 18th, 1921.) 



In a previous paper [Edie, 1919] it was shown that the activity of trypsin as 

 measured by its digestive action on fibrin and on caseinogen is affected to 

 such a different degree by alcohol as to make it seem either that two enzymes 

 are concerned, or, if only one enzyme, that the two substrates are acted on 

 by different groups or side chains, one group being much more sensitive than 

 the other. The effect of heat on the digestion of fibrin and caseinogen by 

 trypsin was next studied. It had been found previously [Edie, 1914] that 

 trypsin when boiled in acid solution still retains much or in some cases all 

 of its power of hydrolysing caseinogen, but in only one case was its action 

 on fibrin tested after heating in this way. Digestion of the fibrin was still 

 noticed, but the amount even in the case of the unheated trypsin was so small 

 that a fresh series of experiments was undertaken. 



The trypsin solutions were generally prepared by extracting finely minced 

 sheep's pancreas with water and a little chloroform for 10 to 14 days and 

 filtering. A httle chloroform was then added as a preservative. The experi- 

 ments were carried out as previously detailed. 



In the experiments described in the previous paper it had been found 

 that in presence of iV/25 to iV/50 HCl the trypsin solutions used retained 

 60 to 100 % of their original digestive power, as tested on caseinogen, after 

 being heated to 100° for three minutes. The same treatment was appUed to 

 the trypsin solutions in this series of experiments and the results are shown 

 in the table. 



In making these extracts, one part of pancreas was extracted with two 

 parts of water in each case. 



In each experiment 1 cc. trypsin + 40 cc. 0-5 % NagCOg + 1 g. fibrin were 

 used on the one hand, digestion being for three hours, and 1 cc. trypsin + 40 cc. 

 1-5 % caseinogen in 0-5 % NagCOg on the other hand, digestion being for one 

 hour. 



The amount of digestion was estimated by precipitating unchanged 

 caseinogen with tannic acid, or by filtering off the undissolved fibrin in the 

 different sets of experiments respectively, and determining the nitrogen in 



(498) 



