LAWS OF ACTION 363 



Similar results were obtained by Adrian Brown * in the 

 study of the action of invertase on cane sugar; he also ex- 

 presses the view that, in the case of alcoholic fermentation 

 and other enzyme actions which do not apparently conform 

 with the law of mass action, the exceptional action "is due 

 to a time factor accompanying molecular combination and 

 change which limits the influence of mass action . . . this 

 theory demands not only the formation of a molecular com- 

 pound of enzyme and reacting substance, but the existence of 

 this molecular compound for an interval of time previous to 

 final disruption and change ". 



Similarly E. F. Armstrong f in studying the action of lac- 

 tase and maltase upon their respective sugars found that 

 while the reaction was in the main logarithmic, both the 

 initial and final stages were linear ; this is explained by the 

 fact that as a result of the combination between the enzyme 

 and the substrate there will be an excess of substrate at the 

 commencement but an excess of enzyme at the end, both of 

 which conditions favour a linear change. 



On calculating the velocity constant for that part of the 

 reaction which is logarithmic it is found that, as a rule, the 

 value steadily decreases, or, in other words, the enzyme ap- 

 pears to become less active. This may be accounted for in 

 one of two ways : either by the assumption that the products 

 of the reaction combine with the enzyme or, by their concen- 

 tration, exercise some inhibiting influence upon the enzyme; 

 or else by assuming that the tendency for the reverse action 

 to take place has a retarding effect. 



That there should be a tendency for the reverse reaction 

 to take place is a perfectly legitimate conclusion ; in fact 

 van't Hoff long ago pointed out that a catalyst which acceler- 

 ates a reaction in one direction must also be able to exert an 

 accelerating effect on the reverse reaction. Consequently the 

 same enzymes which effect hydrolyses should also, under 

 suitable conditions, be able to synthesize. 



The first experimental proof of this was given by Croft 

 Hill, | who showed that when maltase was allowed to act on 



* Adrian Brown: " J. Chem. Soc., Lond.," 1902, 8l, 379. 



t Armstrong: " Proc. Roy.Soc.,Lond.,"B., 1904,73, 500, 516, 526; 74,188, 195. 



jCroft Hill: " J. Chem. Soc. Lond.," 1898, 73, 634. 



