22 'Th'^ Philippine Journal of Science iwu 



The results are practically identical with those given in Table 

 XVI, and show that no different effect is obtained by adding the 

 enzyme solution before coagulation. 



Digestion experiments were carried out in solutions contain- 

 ing sodium bicarbonate in amounts ranging from 0.0 to 0.2 per 

 cent. The presence of this alkali had no effect on the digestion 

 of milk protein. Similar negative results were obtained with 

 concentrations of sodium chloride vazying from 0.10 to 1.0 per 

 cent, although both of these are said to accelerate the digestion 

 of beef by papain.' 



HYDROCYANIC ACID 



Much of the early work that is recorded in the literature of 

 papain must be questioned, because hydrocyanic acid was em- 

 ployed as the antiseptic. It is now known that papain digestion 

 of protein proceeds more rapidly and more completely in the 

 presence of this acid than when toluol or other antiseptic is used. 

 Vines" stated that his experiments "strikingly demonstrate the 

 remarkably favourable effect of the presence of HCN upon the 

 proteolytic activity of papain." Mendel and Blood " have con- 

 firmed this statement in an extended series of experiments with 

 commercial samples of papain, and state that the 



accelerating effect [of HCN] is not limited to the hydrolysis of peptone 

 but is also shown in the digestion of raw and coagulated egg-white, 

 fibrin, edestin, and excelsin whether one take as the gauge of digestion 

 the appearance of trj-ptophane, leucine and tyrosin, the conversion into 

 products not precipitated by hot trichloracetic acid or the rate of solution 

 of insoluble protein. 



No satisfactory explanation of the action of hydrocyanic acid 

 has been advanced. The following series was run with increas- 

 ing amounts of acid to determine its effect on the digestion of 

 milk protein by pure papain. The enzyme was prepared by the 

 alcohol-precipitation method, and was very active. The data and 

 results are showm in Table XIX. 



It may be seen from this table that hydrocyanic acid also in- 

 creased the percentage of milk protein digested by papain. The 

 ratio increased by about 2 units, although no positive color test 

 with bromine water for tryptophane could be obtained. The 

 presence of 0.02 per cent acid was sufficient to give the maximum 

 effect under these conditions, higher concentrations causing no 

 further increase. 



* Private communication from L. D. Johnson. 

 *Ann. Bot. (1903), 17, 606. 

 *Journ. Biol. Chem. (1910), 8, 182. 



