512 



Dr. E. F. Armstrong. 



[Apr. 5, 



being far greater than can be accounted for by the increased " ionisation " 

 or by the greater mobility of the molecules at the higher temperature. 

 Arrhenius supposed that only a part of the total hydrolyte present 

 was really concerned in the hydrolysis : this he termed the " active 

 part." It was arbitrarily assumed that this was a fixed proportion of 

 the total mass at any temperature and that the proportion increased 

 rapidly as temperature rose. 



On the hypothesis that the enzyme combines with the sugar, the- 

 active mass of the sugar will be that portion s of the whole S which 

 is in combination with an amount of enzyme e : it will be convenient 

 to speak of the combination s + e as the active system. 



It is to be supposed that several influences are at work in a solution 

 containing enzyme and sugar : on the one hand, enzyme and sugar 

 molecules seek to combine ; but on the other, the water molecules also 

 tend to unite with the sugar molecules — so that there is, so to speak,, 

 competition between the enzyme and the water for the sugar molecules,, 

 which results in the establishment of an equilibrium depending to* 

 some, though probably a very limited extent, on the proportion rela- 

 tively to enzyme in which the water and sugar molecules are present. *~ 

 The possibility that the products of change also compete for the enzyme 

 must, however, not be left out of consideration. 



It is necessary to consider separately four sets of conditions, viz. : — 



Case I, in which, whatever the amount of sugar present, the quantity 

 of enzyme is relatively small. 



Case II, in which there is a difference from Case I inasmuch as the 

 quantity of enzyme is relatively considerable. 



Case III, in which the amount of enzyme diminishes as the action 

 proceeds. 



Case IV, in which the amount of sugar present is varied. 



Case I. — As hydrolysis proceeds, assuming that the enzyme itself w 

 not affected by the work it does, since the magnitude of the active 

 system depends on the amount of enzyme present, it is obvious that in 

 the initial stages, if the total amount of sugar present S be large com- 

 pared with s, the enzyme will be in presence of enough sugar molecules 

 to establish the maximum possible number of effective combinations : 

 or in other words the magnitude of the active system will remain 

 constant and the change will be expressible, as Brown and Glendinning 

 have pointed out, as a linear function of the time. As hydrolysis 



* The enzymes, it is to be supposed, are colloids, i.e., substances which have but 

 little affinity for water : the stability of the combination s + e will therefore be but 

 to a slight extent dependent on the proportion in which water is present ; whereas, 

 probably, in the case of a combination of a crystalloid, such as an acid, with sugar, 

 tbe proportion in which the components of the system are in equilibrium would, 

 vary to a considerable extent with the concentration. This is known to be the case,. 

 The effect of acids is dealt with in a separate note. 



