ARTICLES 421 



methyl alcohol and glucose giving methyl glucoside and water 

 was reversible. Similar work has been done by Bayliss in the 

 case of the hydrolysis of glycerdl-giucoside. The latter observer 

 has also confirmed the fact that the concentration of enzyme has 

 no effect on position of equilibrium, which, as already stated, 

 shows that the enzyme plays no part in the system in equi- 

 librium. The importance of the amount of water in deter- 

 mining the point of equilibrium has been shown by the work of 

 Armstrong and Gosney (i 914) on the action of lipase on glycerol, 

 oleic acid and olein. These workers showed that the greater 

 the concentration of water the nearer the point of equilibrium 

 was to complete hydrolysis. 



The work of the investigators just mentioned also shows 

 that the same point of equilibrium is reached whatever sub- 

 stances they consider the substrate or products. Thus in the 

 equilibrium obtained under the action of emulsin, they show 

 that the same final condition is reached whether they begin with 

 glyceroglucoside or glycerol and glucose, i.e, the action is 

 reversible. The existence of such reversible reactions is known 

 in nature ; and indeed in Tizard's translation of Nerst's 

 Theoretical Chemistry, the general view is held that all reactions 

 could be shown to be reversible if observers could be sufficiently 

 skilful to demonstrate this. The reversibility of a hydrolytic 

 reaction in itself proves the existence also of synthesis by 

 enzymes, which leads us to a consideration of the various types 

 of reaction which are catalysed by enzymes. 



Reactions Catalysed. — Having reviewed the work relating to 

 the velocity of enzyme action and the factors influencing it, 

 we shall now turn to the consideration of various types of 

 reactions which are catalysed by enzymes. 



Hydrolysis. — ^The hydrolytic power of enzymes was the first 

 to be discovered, and it is but to be expected that most of the 

 work on the subject should have been done in relation to 

 hydrolysis, more especially as it has an important practical 

 bearing on the physiology of digestion and assimilation. 

 Practically all the work hitherto cited has referred to hydrolysis ; 

 indeed by the word enzymes one has almost entirely understood 

 hydrolytic enzymes. 



^Enzymes are, however, concerned in many other processes, 

 but for the most part work on these is in an early stage and 

 has been practically confined to determination of the fact that 

 they do take place. Some of these other reactions are con- 

 sidered below. 



Synthesis. — It has been found — as shown under " Reversi- 

 bility " — that many hydrolytic enzyme actions were reversible, 

 and investigators were thus led to inquire into the synthetic 

 action of enzymes, since the existence of reversibility in a 



