PROTEASES 375 



Fisher employs the following terminology : protease, an 

 enzyme which will hydrolyse any protein or the intermediate 

 decomposition products of proteins ; proteinase (the peptase 

 of Vines), which will hydrolyse the higher proteins only ; and 

 peptase (the ereptase of Vines), which will attack peptones, 

 albumoses, etc. 



The proteinases are readily soluble in salt solution, but 

 only slightly soluble in water, or in 50 per cent alcohol. 

 Their activity is greatest at that degree of acidity natural in 

 the plant extract, but pure aqueous extracts show strong ac- 

 tivity in neutral or slightly alkaline media, -05 per cent hydro- 

 chloric acid, or -3 per cent citric acid inhibiting the action.* 

 In this respect they differ from the protease of Nepenthes, and 

 from animal pepsin, both of which show their greatest activity 

 in the presence of free acid. 



Peptases are readily soluble in water and in aqueous solu- 

 tions of neutral salts. 



Although eraptases are very common in plants, peptases 

 are less common, and have not been found in some cases where 

 they might be expected to obtain, e.g. in protein-containing 

 seeds. Dean's work on Phaseolus vulgaris may be taken as an 

 example.t The seeds of this plant contain much protein which 

 undergoes proteolysis before translocation takes place. But 

 no enzyme has been discovered in the seed which is capable 

 of digesting these proteins ; ereptase, however, which can 

 hydrolyse the proteases derived from the digestion of these 

 seed proteins, is abundant. Dean considers that the proto- 

 plasm plays the part of a peptase, whilst the ereptase may 

 carry the digestion further. 



The plant proteases are less rigid than the corresponding 

 ones from animal sources in respect to their activity in acid or 

 alkaline media. Thus the proteolytic enzyme of Drosera is 

 active in acid, alkaline or neutral media ; papai'n is active both 

 in acid and alkaline media, thus differing from animal pepsin ; J 

 and some proteases will only work provided the reaction be 

 acid, e.g., Nepenthes, malt, mushroom and yeast. The 

 natural reaction of the plant juice is the best to maintain for 

 general experiments. 



* Fisher : " Biochem. Journ." 1919, 13, 124. 



fDean: loc. cit. + Mendel : "Am. Journ. Med. Sci.," 1902. 



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



