Mendel and Underhill — Papain-digestion. 9 



We have searched for leucin, tyrosin and tryptophan among the 

 products of papain digestion under a variety of conditions. In a 

 very large number of experiments we have uniformly failed to 

 detect them. They are therefore, in our opinion, not normal products 

 of the proteolytic action of papain. Enzyme preparations from 

 four different manufacturers were tested in solutions of differing 

 reactions and on the following proteids : casein, fibrin, coagulated 

 egg-albumin, muscle tissue (boiled and unboiled). Only in one 

 series of experiments, viz., those with unboiled muscle tissue, did the 

 products already referred to regularly appear. These cases will be 

 considered in detail below. 



Methods. The digestions were carried out at 35°-38°C. in the 

 presence of two per cent, sodium fluoride, or thymol, to avoid bac- 

 terial decomposition. The reaction of the digestive mixtures varied 

 as described on page 6. At the end of varying periods of time 

 they were filtered and neutralized, when necessary; the fluids were 

 then heated on the water-bath, and after the removal of the charac- 

 teristic albumose-like body which usually separates out, they were 

 concentrated to a small volume and set aside in a cool place to allow 

 bodies like leucin and tyrosin to crystallize out. Finally the residues 

 were extracted with warm alcohol to remove some of these latter 

 compounds and eliminate the greater part of the soluble pro- 

 teids. The alcoholic extracts were in turn concentrated, allowed to 

 stand, and carefully examined under the microscope for crystals of 

 leucin and tyrosin. Trytophan was searched for by the bromine- 

 water test both in the original concentrated neutralized solution and 

 in the final alcoholic extracts. 



The results of over sixty trials made with the four papain prepara- 

 tions (more particularly with papain A, B and D) and with the pro- 

 teids mentioned, were entirely negative so far as the appearance or 

 detection of leucin, tyrosin or tryptophan was concerned. The 

 observations were so concordant in this respect, that it is scarcely 

 necessary to enumerate the variations in time of digestion, the reac- 

 tion of the digestive media, the quantity of enzyme used and other 

 details. Comparisons with control trials always indicated a vigorous 

 digestion in every case. In some instances the digestion was allowed 

 to continue at 35°C. for over a month without altering the results 

 noted. Only with fresh muscle tissue were these tryptic end-products 

 obtained. When hashed muscle (lean beefsteak), washed free from 

 blood with water, was digested with papain in the presence of two 

 per cent, sodium fluoride, the tryptophan reaction was repeatedly 



