SUPPLEMENT 45 



the formation of the ester . by separation of water and its decomposition by 

 taking up water as occurring simultaneously, equilibrium being arrived at 

 when splitting and synthesis proceed at the same rate. Since, however, the 

 rate depends on the concentration of the materials present, it is possible to 

 induce a splitting by increasing the concentration of acid and alcohol ; in 

 other words, the reaction is reversible. If the catalytic agent is unable to 

 alter the equilibrium, hydrolysis of maltose to dextrose, for instance, which 

 under the influence of acids is incomplete and reversible, must also lead to 

 the same equilibrium and be reversible, when effected by an appropriate 

 enzyme (maltase). As a matter of fact, HILL (1898) has proved this. At 

 the same time, it must be noted that the activity of the enzyme must vary 

 greatly according to the degree of concentration of the maltose and the dex- 

 trose ; in one case it will induce hydrolysis, in another synthesis. (It is 

 impossible to discuss in any further detail the fact that the product of the 

 synthesis is isomaltose, which does not quite correspond to the initial sub- 

 stance, maltose.) If continuous removal of the product of the reaction from 

 the mixture be effected, then a complete hydrolysis will be reached or a com- 

 plete synthesis as the case may be. It is readily seen how important this 

 double mode of working of the enzyme, demonstrated by HILL, must be to 

 the organism. 



Synthetic activities, similar to that exhibited by maltose, have been 

 proved to exist in other enzymes also. As examples we may refer to the 

 synthesis of fat out of glycerine, and a fatty acid by lipase, and of amygdalin 

 from grape-sugar, and amygdonitrileglucoside by emulsin. On the contrary, 

 emulsin is unable to form any amygdalin from the products of its complete 

 hydrolysis. 



Irreversible hydrolyses proceeding to total splitting must take place 

 under the influence of enzymes just as completely as under that of acids, but, 

 as a matter of fact, that is not always the case. For instance, the hydrolysis 

 above mentioned, of amygdalin into hydrocyanic acid, oil of bitter almonds, 

 and dextrose in presence of acids, is complete, but it is incomplete when induced 

 by emulsin. The equilibrium in the latter case is described as a ' pseudo- 

 equilibrium ' ; that it is distinct from the true equilibrium occurring in rever- 

 sible actions is shown among other things by the fact that it depends not on 

 the concentration of the amygdalin, but on its amount. Such pseudo-equi- 

 libria, which often appear in enzyme reactions, e.g. in that of diastase, are 

 explained by the fact that the products of splitting act on the enzyme, destroy- 

 ing it or at least rendering it inactive. The splitting goes on again if the products 

 of the reaction be removed or if more enzyme be added. It is obvious that one 

 must not draw any conclusion from such ' pseudo-equilibria ' as to the reversi- 

 bility of the reaction or as to the synthetic activity of the enzyme concerned. 



Several explanations of the accelerating action of the enzyme and of 

 catalytic agents in general have been put forward ; for these we must refer 

 to the literature on the subject, more especially to HOBER'S Physical Chemistry. 

 It will be sufficient if we draw attention to the existence of this power on the 

 part of enzymes. We might express the whole story in a word by saying that 

 the catalytic agent acts as a lubricant to the machine (comp. BREDIG, 1902). 



156, 11. 30-56, for Sufficient evidence . . . later on read More especially we 

 must remember how protoplasm alters in its permeability, alterations brought 

 about, as we know, in a variety of ways. 



157, Lecture XIII as far as p. 161 is combined with Lecture XII in the 2nd 

 German Edition. 



1. 42, for in palms and many other Monocotyledons read in Palmaceae, 

 Rubiaceae, Umbelliferae, Leguminosae, and Liliaceae, 



