372 ENZYMES 



sodium chloride. The solution is filtered and rendered just 

 acid by the addition of acetic acid, whereby a white precipitate 

 of protein is formed, which is filtered off. The acid filtrate 

 has marked proteolytic qualities but has no action on fibrin ; 

 it therefore contains the ereptase. The fibrin-digesting pro- 

 tease (peptase) is in the precipitate ; to recover it, wash the 

 precipitate with a lO per cent solution of sodium chloride 

 slightly acidified with acetic acid. The precipitate is next 

 treated with distilled water and filtered ; the filtrate, which 

 has an opalescent appearance, digests fibrin but has no effect 

 on Witte peptone. In order to ensure the best results, the 

 temperature should be kept as low as possible during filtration. 



GENERAL CONSIDERATIONS, 

 According to Vines, the proteases of plants fall into two 

 main groups : — 



1. Peptase. 



2, Ereptase. 



Peptase hydrolyses proteins to albumose or peptone, but 

 does not act on albumose or peptone whether produced by 

 its own digestion of protein or added in the form of Witte 

 peptone.* 



Ereptase hydrolyses proteins, albumoses and peptones to 

 amino acids, such as leucine and tyrosine. 



Peptase dissolves readily in a saline solution but is hardly 

 soluble in water, whilst ereptase is easily soluble in water. Both 

 may occur in a plant, e.g. the seeds of Cannabis sativa,\ the 

 latex of Carica papaya— \h& enzyme of which is termed papain 

 — yeast, etc.+ In fact the mixture is, or was, commonly termed 

 vegetable trypsin. 



On the other hand, some plants which exhibit proteoclastic 

 properties only have peptase. This is, however, seemingly 

 very rare; Drosera provides an example. § 



Although ereptases 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 



* Vines: "Ann. Bot.," 1905, 19, 171; igoS, 22, 103. 



+ Vines: id., igo8, 22, 103. 



t Vines: id., igog, 23, i. 



§ White : " Proc. Roy. Soc, Lond.," B,, 1910, 83, 134. 



