Further Observations on the Digestion of Fibrin and Caseinogen by Trypsin

Abstract

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 little chloroform was then added as a preservative. The experiments were carried out as previously detailed.In the experiments described in the previous paper it had been found that in presence of N/25 to N/50 HC1 the trypsin solutions used retained 60 to 100 % of their original digestive power, as tested on caseinogen, after being heated to 1000 for three minutes. The same treatment was applied 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 % Na2CO3 + 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 % Na2CO3 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