218 THE HYDROLYZING ENZYMES 



base which exerts a much more intense proteolytic action than trypsin 

 itself. For if we follow the hydrolysis by trypsin, of an alkaline solu- 

 tion of casein by means of the gas-chain (potentiometer) so that we 

 obtain a measure of the changes in the actual hydroxyl ion concentra- 

 tion as the hydrolysis proceeds, we find that the alkalinity of the digest 

 progressively diminishes at a uniform rate corresponding to the 

 formula : 



Velocity = k(a x) 



until a certain Critical Alkalinity is reached, which lies in the 



N 



neighborhood of 10~ 6 N or nnn nnn , below which the velocity of 



1,UUU,UUU 



hydrolysis diminishes very much more rapidly than Wilhelmy's law 

 would indicate. For a given concentration of trypsin the critical 

 reaction is exactly the same when a basic protein such as protamine is 

 employed as when the acid protein, casein, is the substrate. Evi- 

 dently, therefore, this sudden falling off in the velocity of hydrolysis 

 is not due to any relationship of the Substrate to the free alkali in the 

 digest, but rather to a relationship of the Enzyme to the free alkali. 

 The result is, in fact, exactly what one would expect to obtain if the 

 actual catalyst were a compound of trypsin with the alkali. The 

 concentration of the catalyst would remain constant at all alkalinities 

 below those destructive of the enzyme, provided there was a sufficient 

 amount of unneutralized alkali present to combine with all of the 

 trypsin. Directly the concentration of free alkali fell below this limit, 

 however, the concentration of active enzyme would diminish in pro- 

 portion to the diminution of alkalinity, that is to say, in proportion to 

 the extent of hydrolysis, and the velocity of hydrolysis would fall off 

 correspondingly rapidly. 



Since in these two instances we have experimental ground for the 

 belief that the favorable influence of dilute acids or alkalies upon the 

 activity of the enzyme is due to the formation of compounds with the 

 enzyme, we may infer that the mechanism of the acceleration by 

 acids or alkalies is probably the same in other cases. 



THE SPECIFICITY OF THE HYDROLYZING ENZYMES. 



The various enzymes which hydrolyze Disaccharides and Glucosides 

 are highly specific in their action, that is to say, a given enzyme will 

 hydrolyze a particular disaccharide or a particular type of glucoside 

 and no other. A very beautiful example of the specific relationship 

 which subsists between the structure of a glucoside and the nature 

 of the enzyme which attacks it is that afforded by the enzymatic 

 hydrolysis of the various Methyl Glucosides. Four of these glucosides 

 are known, namely a-methyl-1-glucoside, and /3-methyl-l-glucoside, 



