Mendel and Underhill — Papain-digestioji. 5 



— contrary to the statements of several writers — peptones, /. e., 

 biuret-giving compounds not precipitable by ammonium sulphate 

 or zinc sulphate, are formed in considerable amounts. The latter 

 were separated from digestive mixtures and their physiological 

 action was investigated. Previous to this Neumeister' only had 

 directed attention to this point. His report is, however, very scanty, 

 and the commercial preparation of " papayotin " which he used must 

 have been rather inactive ; for although it dissolved coagulated egg- 

 white in an alkaline mixture, it failed to digest fresh fibrin or to act 

 in acid or neutral solutions. He arrived at no definite conclusion 

 regarding the nature of the enzyme. 



The present investigation is the outcome of an attempt to isolate 

 the end-products of the action of papain upon purified j^roteids. 

 Relying upon such statements as have been introduced into the 

 literature on this subject, we had expected to find a marked resem- 

 blance in character between the products formed by trypsin and 

 those resulting from papain pi'oteolysis. Our experiments, on the 

 contrary, soon indicated that pronounced differences exist. From the 

 data accumulated we feel justified in reporting some additional 

 features regarding the action of the papaw enzyme. We have not 

 been fortunate enough to secure specimens of the fruit itself for 

 stud}^ ; but the results obtained with four commercial preparations 

 from different sources are fairly concordant and characteristic and 

 give no occasion to suspect the extensive admixture of other enzymes. 

 These preparations will be referred to below as Papain A, B, C, and 

 D; they were bought under the names of "Papoid," " Caroid," 

 "Papain (Lehn and Fink's)," and "Papain (Merck's)" respectively. 

 Our observations will be considered under four chapters in the part 

 following. 



I. The Influence of the Reaction on the Proteolytic Action 



of PapcCm. 



A survey of the literature on the action of papain shows that the 

 observers have by no means been agreed regarding the conditions of 

 reaction under which proteolysis proceeds favorably. Wurtz, the 

 earliest careful investigator of this point, and Chittenden, who made 

 the most exhaustive study (with "papoid"), both found the enzyme 

 active in acid, alkaline and neutral media, as already indicated. 

 Similar observations were made by Polak^ with two papain prepara- 



^ Neumeister : Zeitschrift fiir Biologie, 1890, xxvi, p. 82. 

 -Polak: Jahresbericht flir Thiercliemie, 188'i, xii, p. 254. 



