150 Scientific Proceedings (84). 



89 (1267) 



Influence of certain electrolytes upon the course of the hydrolysis 

 of soluble starch by malt amylase. 



By H. C. Sherman and Jennie A. Walker. 



[From the Laboratory of Food Chemistry, Columbia University.] 



The rate of formation of reducing sugar (maltose) from soluble 

 starch by purified malt amylase of diastatic power equivalent to 

 about 1 ,600 on Lintner's scale, both in neutral solution containing 

 no added electrolyte and with the addition of regulated amounts 

 of hydrochloric or phosphoric acid or of primary potassium phos- 

 phate, was investigated from the beginning of the reaction to 

 completion or until the hydrolysis is no longer measurable. 



When the activating electrolyte was added in such amount 

 as to give optimum or nearly optimum concentration of hydrogen 

 ion, the action of the enzyme was increased not only in the earlier 

 stages but throughout the entire range investigated. The greater 

 the concentration of enzyme the less the apparent favorable 

 effect of the added electrolyte. 



The same optimum hydrogen ion concentration, C H io -4-4 

 (P H +44), was found to hold for each of the acid electrolytes tested 

 and appears to hold throughout the course of the hydrolysis. 

 (With neutralized starch substrate used in this laboratory the 

 amount of acid or acid phosphate required for optimum activation 

 is about half as much for one per cent, as for two per cent, starch.) 



When more than the optimum amount of acid was added the 

 hydrolysis proceeded at less than the optimum rate throughout; 

 when less, the initial rate was better sustained. This difference 

 was most pronounced in the case of hydrochloric acid; less with 

 phosphoric acid; least in the case of acid phosphate ("buffer 

 effect"). 



With initial concentrations of 1 per cent, soluble starch it was 

 found that, throughout the first half of the hydrolysis, or up to a 

 yield of half the theoretical amount of maltose, the rate of maltose 

 formation from soluble starch was found to be proportional to the 

 concentration of substrate (in the form of starch and dextrin) still 

 remaining at any given time, at least in solutions containing 

 avorable amounts of acid or acid phosphate. 



