DIASTASE 359 



Also, the amount of diastase is always greater in starch leaves 

 than in sugar leaves and the same holds for insolated leaves 

 containing much starch, as compared with shaded leaves con- 

 taining little or no starch.* 



ISOLATION OF DIASTASE. 



To obtain a relatively large quantity of diastase, germinated 

 barley gives excellent results. The grains are soaked in water 

 for twelve hours, and then spread out in a thin layer on a tray 

 which is placed in a warm, damp — but not too damp — place. 

 When the radicles are about one quarter of an inch long, the 

 grains may be dried at a temperature not exceeding 40° C. ; 

 they are then ground up as finely as possible. The powder is 

 mixed thoroughly with about four times as much water, and 

 allowed to stand for an hour or two, the mixture being well 

 shaken up periodically. The fluid is then filtered off and 

 evaporated in a vacuum to a small bulk ; this concentrated 

 solution is poured into an excess of absolute alcohol, whereby 

 the diastase, and other substances, are precipitated. The 

 precipitate is filtered off, and washed with alcohol. The 

 diastase thus obtained may be partly purified by dissolving 

 in water and re-precipitating with alcohol. 



Although diastase occurs in green leaves, it is often difficult 

 to demonstrate its presence in an aqueous extract of the fresh 

 tissue. If the leaves be dried and ground to a very fine powder, 

 the above procedure should yield positive results ; if not, then 

 the powdered leaves may be added directly to a one per cent 

 solution of starch paste or to a little dry starch suspended 

 in water in a watch glass. The disappearance of the starch, 

 as indicated by the iodine reaction, and the corrosion of the 

 solid starch grains, point to the presence of diastase. 



The action of this enzyme is promoted by the presence of 

 acids, e.g., hydrochloric or citric, but if too much acid be added, 

 the action is inhibited. 



To study the action of diastase on starch a mixture of 

 these two substances may be tested from time to time with 

 iodine solution. 



* Eisenberg : " Flora," 1907, 97, 347. 



