STUDIES ON ENZYME ACTION. 

 XVIII. The Saccharogenic Actions of Potato Juice. 



By grace McGUIRE and K. GEORGE FALK. 

 (From the Harriman Research Laboratory, the Roosevelt Hospital, New York.) 



(Received for publication, November 14, 1919.) 

 INTRODUCTION. 



The results of enzyme studies on a number of fresh and dehydrated 

 vegetables were communicated in a previous paper.^ In connection 

 with the experiments on amylase, it was there stated that: "Potato 

 juice, when tested for amylase by the method used with the other 

 vegetable juices, gave an end-point which was so uncertain and 

 difficult to determine that a different method had to be employed for 

 it." In this paper are presented the results of a more careful study of 

 potato amylase. Evidence is given showing the occurrence of a 

 sucrase, and of a certain amount of sucrose or raffinose in potato 

 juice. 



Experimental Method. 



An extended study of potato amylase was published by Doby.^ 

 Attempts were made to repeat his work, but it was soon found that 

 his observations were incomplete. In his work a series of tubes 

 containing varying amounts of potato juice and Lintner soluble 

 starch were set up for each experiment. After incubation, the super- 

 natant liquid in each tube was pipetted from a residue, which sepa- 

 rated as a rule, and was tested with iodine. The measure of the 

 action was given by the tube in which no starch test was given with 

 the iodine. Doby stated that the residue or precipitate contained 

 no starch, but he did not present any experiments of his own in this 

 connection. This statement apparently is based upon the work of 



1 Falk, K. G., McGuire, G., and Blount, E., /. Biol. Ghent., 1919, xxxviii, 229. 



2 Doby, G., Biochem. Z., 1914, Ixvii, 166. 



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