G. MCGUIRE AND K, G. FALK 223 



The two series of actions, on the juice constituents and on the 

 added starch, show definite differences which are also brought out in 

 Table II. 



In the first place, it is interesting to note that both sets of actions 

 show maxima at pH 6 to 7, approximately the acidity of the natu- 

 rally occurring material. This was also observed with the amylase 

 actions of the vegetable juices reported in the previous paper. 



In comparing the two sets of actions, at pH 4, the action on the 

 juice constituents is much greater than on the added starch; approx- 

 imately the same at pH 6 to 7 ; and reversing at pH 8 where the action 

 on the added starch is much greater than on the juice constituents 

 themselves. 



The increase in reducing substances of the juice alone and the 

 juice with added starch is not, in all probability, a simple action. 

 The nature and amounts of the possible products formed were not 

 investigated, so that an accurate quantitative comparison is not fea- 

 sible. The action on added starch, showing a maximum at pH 6 to 

 7, may be compared to maxima for the juices of the cabbage, carrot, 

 and white turnip at about pH 6, for yellow turnip, ranging from 

 pH 4 to 7; for pancreatic amylase,^" pH 7; for malt amylase,^" pH 

 4.4 to 4.5; and for Aspergillus oryzcB amylase,^" pH 4.8. This action 

 of potato juice on added starch is without doubt an amyloclastic 

 action. The increase in reducing action of the juice alone may, 

 however, be of more complex nature. The results shown in Tables 

 I and II indicate the possibiHty that, in addition to the amylase act- 

 ing upon the starch of the juice, other enzymes may be acting upon 

 other constituents. This view was tested experimentally, and it was 

 found that at least a sucrase and also either sucrose or rafi&nose or 

 both were present, and that presumably the sucrase hydrolyzed the 

 sucrose or rafiinose. No evidence of the presence of a maltase was 

 obtained. 



Sucrase and Maltase Experiments. 



In order to test for the presence of a sucrase in potato juice, series 

 of experiments similar to those described were set up including addi- 

 tional series containing enough sucrose to ro.ake 1 per cent solutions. 



^^ Sherman, H. C, Thomas, A. W., and Baldwin, M. E., /. Am. Chem. Soc, 

 1919, xli, 231. 



