United States Department of Agriculture, 



BUREAU OF CHEMISTRY Circular No. 60. 

 H. W. WILEY, Chief of Bureau. 



A THEORY OF THE INFLUENCE OF ACIDS AND ALKALIS ON THE 

 ACTIVITY OF IN VERT AS E. 



By C. S. HUDSON, Assistant Chemist. 



In alkaline solutions invertase shows no activity, in weakly acid 

 solutions its enzymotic power reaches a maximum from which it 

 decreases with increasing acidity. The simplest theoretical inter- 

 pretation of this striking fact is that acids and alkalis combine with 

 invertase by the principles of the law of mass-action and prevent 

 it from inverting cane sugar. In the following calculations this 

 hypothesis will be tested. If invertase combines with both acids 

 and alkalis it is an amphoteric electrolyte and may be assumed to 

 dissociate as follows: 



(1) Invertase ^H + anion (acidic dissociation). 



(2) Invertase *^OH f + cation (basic dissociation). 



If a units of invertase are dissolved in a unit volume of a solution 

 containing hydrogen and hydroxyl ions in the fixed concentrations 

 (H) and (OH'), it will form x units of anion and y units of cation, 

 leaving a-x-y units of undissociated invertase. The mass-action 

 law requires the fulfilment of the following conditions when equi- 

 librium is attained : 



( 



a-x-y) 



The quantity a-x-y is the concentration of uncombined or undis- 

 sociated invertase, and it is here assumed that the enzymotic activity 

 is caused by this substance and is proportional to its concentration. 

 Solving (3) and (4) for a-x-y gives- 

 Activity (i. e., a-x-y) = 



H 



where K w is the dissociation constant for water. This formula con- 

 tains the three coefficients a, K lt and K 2 , which are of unknown 

 45663 Cir. 6010 



