THE NATURE OF ENZYME ACTION 289 



maltose by fermentation with living yeasts. The importance of 

 the synthetic aspect of enzyme action has been pointed out by 

 Croft Hill. The various enzymes present in living cells may 

 indeed be responsible for the building-up processes taking place 

 therein. Take such a case as the formation of starch from sugar 

 in the green leaf. Even supposing that less than 99 per cent, 

 of the glucose or maltose produced in photosynthesis is con- 

 verted by the intracellular amylase into starch, the fact that 

 starch is insoluble and is at once deposited out of the reacting 

 system renders possible a considerable amount of conversion in 

 a reasonably short time. 



Before passing on to the subject of the next section it is 

 advisable to refer to another kind of equilibrium, which is of a 

 somewhat more complex nature than that already discussed, 

 and which is met with in certain instances, especially where the 

 products of the reaction have a specific retarding action on 

 the enzyme. Such a case is that of amygdalin and emulsin, as 

 investigated by Tammann. These cases differ from what may 

 be called " true " chemical equilibrium in that the enzyme itself 

 forms part of the system when in equilibrium. This is shown 

 by the fact that addition of more enzyme to a solution which 

 has arrived at a stationary condition causes further progress of 

 the reaction. It is not correct to call these cases " false " equi- 

 librium, since they show all the properties of a true equilibrium, 

 such as alteration by adding more substrate, removing products 

 of reaction, dilution or concentration or change of temperature, 

 with also that characteristic already referred to, viz. additional 

 change by adding more enzyme. It is in such instances that 

 the question of compounds between enzyme and substrate or 

 products of reaction comes more prominently under our notice 

 but this aspect of the phenomena will be discussed later. 



Velocity of Reaction 



Practically, all enzyme actions with which we have to deal 

 are unimolecular, or, in other words, their velocity may be 

 represented by the rate of change of one molecule into two 

 or more. The great majority of them, in fact, consist in the 

 splitting up of a molecule by introducing into it the elements 

 of water. 



To simplify matters we will commence by neglecting the 



19 



