QUANTITATIVE RELATIONSHIPS IN HYDROLYSIS 207 



attempt to re-isolate an enzyme after it has acted upon a measured 

 amount of substrate, in order to determine the loss of activity it may 

 or may not have sustained during the reaction, can possibly be success- 

 ful, therefore, in the present inadequate state of our knowledge and our 

 manipulative technique. 



A variety of the hydrolyzing enzymes are not only inactivated, 

 temporarily or permanently by heat, but also by exposure to light 

 and particularly to Ultraviolet Light. Solutions of enzymes are also 

 temporarily inactivated by intense agitation of the solution of such a 

 character as to give rise to excessive formation of foam. It is then 

 found that the enzyme has become concentrated in the foam and is 

 restored to the solution when the foam subsides. A portion of the 

 enzyme also, under these circumstances, becomes temporarily attached 

 to the surface of the containing vessel. This phenomenon is not 

 peculiar to enzymes, however, for it is exhibited, in greater or less 

 measure, by all those substances which, when dissolved in water, reduce 

 the Surface-tension of an air-water interface. For example it is dis- 

 played to a striking extent by the various Saponins or by Bile-salts. 

 (See Chapter XIII.) This liability to become concentrated at liquid 

 surfaces is probably the explanation of the striking tendency, to which 

 reference has already been made, of the various hydrolyzing enzymes 

 to be carried down in association with precipitates which form in their 

 solutions. They are similarly "adsorbed" by such substances as 

 animal charcoal or by insoluble proteins. 



THE QUANTITATIVE RELATIONSHIPS IN HYDROLYSIS BY 



ENZYMES. 



We have seen that when cane-sugar is hydrolyzed by acids the 

 relationship between the amount of unaltered sugar in the system and 

 the velocity of change is rather a simple one. The two quantities, the 

 amount of unaltered sugar and the velocity of decomposition, are 

 simply proportional to one another and stand in a constant ratio to 

 one another throughout the reaction. The case is not so simple when 

 the hydrolysis is brought about by Invertase. It will be recollected 

 that we regard the rapid hydrolysis of cane-sugar by acids as being due 

 to the formation of a compound between the cane-sugar and the acid, 

 this compound being very easily attacked by water. At any instant 

 the percentage of acid thus combined is almost infinitesimal. The 

 amount of this compound is, as usual in such cases, directly propor- 

 tional to the concentrations of its components, the acid and the sugar, 

 so that we have: 



Concentration of sugar-acid compound = constant X concentration of acid 

 X concentration of sugar. 



