100 ENZYMES 



digestion was carried on in a beaker, and in the other in a 

 dialysing tube immersed in running water so that the maltose 

 dialysed out. 



TABLE XVII. 



Ecto-enzymes generally have a catalytic function. The by- 

 products of their activity are removed as rapidly as they are 

 formed. Many endo-enzymes have for the most part an anabolic 

 activity. They are brought into contact with simple compounds 

 and proceed to build them into more complex substances. All 

 enzymes have both breaking - down and building - up func- 

 tions. The conditions under which they work determine their 

 function. 



A peculiar phenomenon has been noted in this connection, 

 namely, that the substance built up by an enzyme may not be 

 quite the same as the complex substance originally broken down 

 by it. Maltase, for example, splits maltose into molecules of 

 glucose, but the substance formed by the action of maltase on 

 glucose is not maltose but its ft form, isomaltose. On the other 

 hand, isomaltose is split by emulsin into glucose, while emulsin 

 causes two glucose molecules to unite to form maltose. This is 

 explained by supposing that the nature of the enzyme-substrate 

 complex influences the rate of the reaction. If HC1 is used as 

 catalyst, the equilibrium point is reached with glucose, maltose, 

 and isomaltose present in the same proportions, irrespective of 

 the original proportions present in the substrate. The point of 

 equilibrium is changed by the enzyme. If maltase is used, the 

 proportion of maltose is diminished, but if emulsin is the enzyme 

 employed the point of equilibrium is shifted towards isomaltose. 

 The whole subject requires re-examination from the point of 

 view of colloid chemistry, especially with regard to the influence 

 of P H on activity. The following table gives the optimum P H for 

 certain enzymes : 



