204 THE HYDROLYZING ENZYMES 



must hold good for a catalyzed as for an uncatalyzed hydrolysis, so 

 long as the concentration of the catalyzer is kept unaltered. 



Since the quantity of the acid-sugar compound is also proportionate 

 to the concentration of the acid, it follows that with varying concen- 

 trations of acid the velocity of hydrolysis must also vary directly 

 with the concentration of acid. In other words the value of "k" in 

 the above equation is directly proportional to the concentration of 

 catalyst, or: 



Velocity of hydrolysis = kf (a x) 



where "f" is the concentration of the catalyzer. In fact so accurately 

 does this relationship obtain that the ratio of the velocity of the 

 hydrolysis of cane-sugar to its concentration is very commonly 

 employed as a means of measuring the quantity of free acid (= hydrogen 

 ions) which is present in a solution. 



So much for the hydrolysis of cane-sugar and of other disaccharides 

 by acids; but cane-sugar is also hydrolyzed by an Enzyme, to wit, 

 Invertase. This enzyme is found in yeasts, in certain moulds and 

 bacteria, in green leaves and young twigs, in some fruits and in germi- 

 nating grains. In mammalia, it is sometimes found in the human 

 gastric juice, but not in the gastric juice of cows. It is also found in 

 weak concentration in other organs. It may be extracted from yeast- 

 cells with water, provided the cells have previously been subjected to 

 the action of some Plasmolyzing Agent, or agent which will break up or 

 enhance the permeability of the limiting membrane of the cell, such as 

 alcohol or ether. The invertase can then be precipitated from its 

 watery solution by alcohol, and this precipitate, in nearly neutral 

 solutions in which hydrolysis would otherwise be excessively slow, 

 rapidly decomposes cane-sugar into its constituent hexoses. 



It should be clearly understood that, as in the case of the other 

 enzymes, we possess no clue which enables us to decide whether there 

 is only one or whether there are many invertases. We do not know 

 anything whatever concerning the chemical composition of invertase. 

 Our only means of recognizing this enzyme is by the property which it 

 possesses of hydrolyzing cane-sugar, giving rise to Glucose and Fructose. 

 Any agent which can be extracted from living tissues which does this 

 and is inactivated by high temperatures we call invertase. It is quite 

 conceivable that many different substances can accomplish this 

 hydrolysis. The activity of an invertase preparation is no guide to its 

 individuality, because in the absence of any knowledge of the chemical 

 properties of invertase, we cannot estimate the purity of any prepara- 

 tion. We can recognize certain impurities, such as phosphates, pro- 

 teins and so forth in a preparation of invertase, and we can remove 

 some of them, wholly or partially. But when easily recognizable 

 impurities have been removed, we cannot tell whether the residuum is a 

 pure material, that is, a chemical individual, or a mixture of different 



