PROTEOLYTIC ENZYMES 485 



litres of ice cold 90 per cent alcohol. The precipitate was 

 filtered off, washed with absolute alcohol and twice with 

 ether, and then air-dried. The last traces of ether were re- 

 moved in a vacuum desiccator. The resulting powder repre- 

 sented 4-4 per cent of the original dried roots. 



GENERAL CONSIDERATIONS. 



Proteases are slightly soluble in water and in 50 per cent 

 alcohol ; they are, however, readily soluble in 10 per cent 

 sodium chloride solution in water. Peptidases are readily 

 soluble in water whilst amidases are but sparingly soluble. 



The proteolytic enzymes of plants are less rigid than 

 those of animal origin in respect to their activity in acid or 

 alkaline media. Thus it is stated that the proteolytic enzyme of 

 Drosera is active in acid, alkaline or neutral media ; papain is 

 active both in acid and alkaline media, thus differing from 

 animal pepsin ; and some proteases will only work provided the 

 reaction be acid, e.g. Nepenthes* malt, mushroom, and yeast. f 

 For this reason it is not possible to divide plant proteases 

 into a pepsin group, which are active only in an acid medium, 

 and a trypsin group which are active only in an alkaline 

 medium. 



In general terms the proteases are most active at Pg 5-0. 

 There is, however, much variation ; thus the optimum reaction 

 of malt protease varies between Pg 37 to Pg 4-2 ; of the pepti- 

 dases, the optimum reaction of papain is about Pg 5"0 ; whilst 

 that of asparaginase is P^ 7-0. These values, however, vary 

 with the substrate ; thus Willstatter found that the peptidases, 

 papain and bromelin, hydrolyse fibrin best at Pg 7-2, and 

 peptone best at P^ 5-0, which indicates that the optimum P^ is 

 not entirely a function of the enzyme itself but is dependent 

 also on the nature of the substrate. 



It will be noticed that these values are either neutral or 

 acid ; the reaction of plant juices Ukewise are neutral or acid, 

 wherefore the natural reaction of the plant juice is the best 

 to maintain for experimental purposes. 



♦Fisher: " Biochem. Jourii.," 1919. I3» 124. 

 t Vines : " Ann. Bot.," 1905, 19, 171. 



