78 EXPERIMENTAL OBSERVATIONS ON 



DISCUSSION OF EXPERIMENTAL RESULTS ON VELOCITY OF 

 REACTIONS INDUCED BY ENZYMES 



It is clear from the foregoing account of the experimental 

 results obtained by different authors, that in the case of the 

 enzymes the simple logarithmic law fails widely to suit the general 

 course of the reaction. The formula of Henri, although it fits 

 the earlier portion where the velocity is expressed as a linear 

 function, or the portion where the curve increases above the 

 logarithmic law, fails entirely to cover the portion, occupying in 

 some cases the greater part of the reaction, where the products 

 of digestion retard the reaction. Its form shows that it is based 

 in fact on an accelerating action of these products. Finally, the 

 mode of treatment adopted by Armstrong, while it gives a verbal 

 explanation of the cause of the variations at different stages in 

 the reaction, fails to unite these into one formula, or to give any 

 expression which will show the velocity of the reaction at any 

 stage. 



It may be inquired, therefore, whether any assumption has 

 been made in the deduction of the velocity equation for such 

 reactions as we have been considering which has been the means 

 of introducing the differences between theory and experiment. 



The equation from which the simple logarithmic expression, 



k = ~ log - , is derived is - = & (a x), which simply ex- 



t Ct X U>t 



presses that the rate of change at any moment is proportional 

 to the concentration of the unchanged substratum at that moment. 

 The entire action of the enzyme, as far as the formula is con- 

 cerned, is contained in the constant k ; the more powerful the 

 enzyme the greater is the value of k, and the less powerful the 

 less is the value of k. Regarding the ferment as acting by 

 reducing the resistance to reaction in the system, as described 

 above, we may regard k as the conductivity factor in the reaction. 



dx 

 Hence by writing -v- = k (a-x), we have assumed that the effect 



of the enzyme upon the conductivity is constant throughout the 

 reaction. Expressed in another way, the assumption has been 

 made that throughout the whole of the reaction, no matter what 



