244 



[Vol. 6 



ANNALS OF THE MISSOURI BOTANICAL GARDEN 



with water) is incubated. If the figures in the third column, 

 which represent the diluted juice boiled at the beginning of the 

 experiment to kill the enzyme, are compared with those in the 

 second, it will be seen that there is a considerable increase in 

 reducing sugars. This is probably due to conversion, by the 

 enzyme, of dextrins in the juice, to reducing sugars. The 

 differences in this respect are less in the case of the seed potatoes, 

 which corresponds with their lower enzyme activity. 



The activating effect of boiled potato iuice upon the diastase 



has been observed by Doby 



The table 



below (table n) shows some results obtained by the 



this poii 

 perman 



it. The figures represent cubic centimeters of potassium 

 ;anate used in titrating the dissolved cuprous oxide. 



The "enzyme" used is that obtained by precipitation with 



alcohol, as has already been described. 



TABLE II 



EFFECT OF BOILED JUICE UPON THE ACTIVITY OF POTATO DIASTASE 



N 



No. cc. — KMn0 4 used in titrating Cu 2 



Sample 



Enzyme-h 



starcl 



1 



Enzyme + 



starch + boiled 



filtered juice 



Boiled 

 filtered juice 



Difference 

 due to enzyme 



in presence 

 of boiled juice 



1 



2 

 3 

 4 

 5 





 

 



.4 

 .3 



4.1 



5.6 



2.2 



26.0 



5.9 



2.8 



4.3 



.6 



24.6 



4.9 



1.3 

 1.3 

 1.6 

 1.4 

 1.0 



From the figures given, it seems that the activity of diastase 

 of potatoes depends upon some substance contained in the juice, 

 but not precipitated by alcohol. It is well known that a number 

 of substances have an activating effect upon diastase, but it has 

 been generally considered that the enzyme when alone would act 

 upon starch, and as far as the author is aware, no one has before 

 presented evidence to show that this is not always the case. 



In the first tests made, no activity whatever was observed 

 when the enzyme alone was added to the starch solution, but in 



