v] HYDROLYZING ENZYMES 73 



Take the residue of leaves and pound (but not finely) in a mortar and then wash 

 thoroughly with distilled water. Filter through muslin and press free from water 

 (this process extracts most of the protein). Boil the residue with 100 c.c. of water and 

 filter. To the filtrate add iodine. At first the colour may disappear owing to the 

 presence of protein in solution in addition to the starch. When more iodine is added 

 a deep blue coloration is formed. 



PLANT ENZYMES WHICH HYDROLYZE CARBOHYDRATES. 



Diastase. In the plant starch may be regarded as a reserve product. 

 It is synthesized from sugar, and may be again hydrolyzed into sugar. 

 It can be shown experimentally that starch is converted into glucose by 

 boiling with acids, but in the plant the hydrolysis of starch is catalyzed 

 by the enzyme, diastase. Although the reaction is doubtless of con- 

 siderable complexity, it may, broadly speaking, be represented as 



follows : 



(C 6 H 10 5 ) H +H 2 ^ (CeH^O^ + C^H^On 

 Dextrin Maltose 



Thus the final products under these conditions are dextrin and the 

 disaccharide, maltose ; and not glucose. 



It is reasonable to assume that cells which contain starch also either 

 contain, or are capable of producing, diastase. But the amount of 

 diastase present, or at any rate capable of being extracted, varies in 

 different tissues. Diastase, like most enzymes, is soluble in water. In 

 many cases, however, a water-extract from fresh crushed tissues in which 

 diastase occurs, will not contain any appreciable amount of enzyme. 

 This is sometimes due to the fact that the protoplasm does not readily 

 yield up the enzyme until it has been killed. If the tissues are dried at 

 a moderate temperature (30-40 C.) both the powdered leaves them- 

 selves and a water extract are fairly rich in diastase ; or, if the living 

 tissues are macerated and extracted with water to which chloroform 

 has been added, the cells die more rapidly and yield up the enzyme to 

 the solvent. From such a water extract, a crude precipitate containing 

 the enzyme may be obtained by addition of alcohol. For obtaining the 

 maximum results with diastatic activity in leaves, a water extract 

 should be made after they have been killed, either by drying, or by the 

 action of toluol or chloroform. 



It has been shown (Brown and Morris, 5) that in leaves which con- 

 tain tannin, the presence of the latter largely inhibits the action of the 

 enzyme and may be the cause, in such cases, of an entire lack of activity 

 in the extract. 



