1919] 



MCGINTY — DIASTASE ACTIVITY OF SOLANUM TUBEROSUM 239 



these tubers, except the largest size, which was practically 

 mature, were still in an active, growing condition, and it is be- 

 lieved that they really represented not only different sizes but 

 also different stages of development. This should be especially 

 true in the case of the enzyme activity determinations, as it 

 was necessary in making these to use a rather large number of 

 the tubers to obtain the juice needed, thus providing a com- 

 posite sample. 



Diastase activity. — Two or three methods of obtaining the 

 enzyme were tried before a satisfactory one was found. When 

 the potatoes were sliced and dried by means of alcohol and 

 acetone, according to the method used by Davis ('15), and then 

 finely ground in a mortar, extracted with water, and the 

 enzyme precipitated with 95 per cent alcohol, the diastase so 

 obtained was apparently not active enough to make the method 

 satisfactory. 



A method whereby the enzyme was precipitated by alcohol 

 from the pure juice of the potato was then tried. The juice was 

 obtained by quickly grating the tubers, grinding the material 

 in a mortar with carborundum, squeezing the juice out by means 

 of a tourniquet of cheese-cloth, and finally filtering through 

 asbestos and filter-paper. The filtering was done in order to 

 remove the starch present. The enzyme obtained from this 

 juice by precipitation with alcohol apparently possessed no 

 activity whatever, and it was finally decided to use the juice 

 itself, as preliminary tests had shown it to be quite active 

 diastatically. The fact that the juice of the potato has consid- 

 erable activating influence upon the diastase, as found by Doby 

 ('14), was confirmed, and this no doubt accounts for the inac- 

 tivity of the alcohol-precipitated enzyme. 



In determining diastatic activity, 20 cc. of the fresh juice 

 were added to 100 cc. of a .25 per cent soluble starch solution 

 in a 250-cc. Erlenmeyer flask, 2 cc. of toluol added, and the 

 flasks placed in the incubator and kept at 45° C. for 12 hours. 

 At the end of this time the flasks were placed in boiling water 

 for 10 minutes to kill the enzyme. 



At the same time checks were made on the above by substitut- 

 ing 100 cc. of water for the starch in two flasks, incubating one 



