ENZYMES AND THEIR ACTION 4o7 



besides iii^-nv bacteria. Its action is the hydrolysis of cane- 

 sugar with the formation of dextrose and levulose, according to 

 the equation 



CiA,Oji + H,,0 = C,Hj,0,; + C,Hj,0, 



Cane-sugar. Dextrose. Levulose. 



Glucase occurs in the seed of the Maize. It converts 

 maltose into dextrose. 



Cytase is chiefly known in the germinating grain of the 

 barley, wiiere it is secreted by the seutellum together with the 

 diastase. It dissolves the walls of the cells of the endosperm, 

 setting them free and giving a curious mealy character to the 

 grain. Its presence is suspected in the Palms, where large 

 reserves of cellulose are found in the hard endosperm walls. 

 The embryo dissolves these walls and absorbs their products, 

 but whether the ferment has a free existence is not yet settled. 

 Cytase abounds in certain Fungi belonging to the genus 

 Bofrytis. 



Pectase is but little known, and its function is not very clear. 

 It is recognised by its power of forming vegetable jelly from the 

 pectic bodies of the cell- wall. This jelly appears to be a com- 

 pound of pectic acid with calcium. 



The proteolytic enzymes pepsin and trypsin appear both to 

 be represented in plants, though to what extent the former exists 

 is somewhat uncertain. It is the enzyme which is found in the 

 insectivorous plants Droser^a, Dioncea, and others, and it con- 

 verts the native proteids of the insect's body into peptones, wliich 

 are absorbed by the leaf. It only acts in the presence of a weak 

 acid and is only formed by the plant when the gland has been 

 stimulated by the absorption of nitrogenous matter. Trypsin 

 has a much wider distribution, being known to exist in the fruits 

 of the Papau {Carica Pajjaya), the Fig, a variety of the Melon 

 (Cucumis utilissimns), and the Pine-apple {Ananassa sativa), 

 also in many seeds, such as those of the Hemp, Flax, Barley, 

 and Lupin. In the latter structures it is of especial value in the 

 processes of germination, feeding the young seedling with nutri- 

 tive proteid or nitrogenous matter until the time when it is able 

 to begin the constructive processes. 



It acts upon insoluble proteids, forming from them albumoses, 

 peptones, and amides, such as leucin, tyrosin, and asparagin. 

 The medium in which it works varies according to the soiu^e 

 of the enzyme ; that prepared from the Papau requires a slightly 

 alkaline one, that from the Lupin works best in a weak acid. 



