PROCEEDINGS OF 



THE ROYAL SOCIETY. 



Suction B. — Biological Sciences. 



Studies in the Mechanism of Enzyme Action. I. — Role of the 

 Reaction of the Medium in Fixing the Optimum Temperature 

 of a Ferment. 



By Arthur Compton, M.B., D.Sc, Mackinnon Student, British Medical 



Association Scholar. 



(Communicated by Prof. B. Moore, F.R.S. Eeceived July 24, 1920.) 



, Previously, it has been shown for the enzyme iiicdtase — enzyme requiring 

 an acid medium in which to act to best advantage — that increase in the 

 acidity or hydrogen ion concentration of the medium in which the enzyme 

 acts, beyond the optimum acidity, leads to a fall of optimum temperature.* 

 The mechanism of this temperature effect appears clearly to be due to a 

 certain disablement of the enzyme, brought about by tlie presence of excess 

 of acid, for the fall of optimum temperature which occurs is rigorously 

 proportional to the decrease of enzymic activity, estimated at the optimum 

 temperature point ; which decrease of activity is itself a function of the 

 degree of acidity of the medium in excess of that necessary to produce 

 optimum activation.* Being in this way a disablement effect, the question 

 arises whether, by adding to the quantity of enzyme in action, the lowering 

 of optimum temperature which takes place can be controlled. To answer 

 that question, the experiments described in the present paper were under- 

 taken. 



For the investigation, the enzyme used is the maltase of Aspergillus oryzce, 

 the same preparation being employed as studied by us in two previous 

 communications,f a specially active specimen of takadiastase, purified by 

 repeated solution in water and reprecipitation by alcohol. 



Fig. 1, based on one of the* foregoing communications,* indicates the 



* Arthur Compton, 'Eoy. Soc. Proc.,' B, vol. 88, pp. 408-417 (1915). 

 t Arthur Compton, ' Eoy. Soc. Proc.,' B, vol. 88, pp. 258-263 (1914), and loc. cit. 

 VOL. XCII. — B. B 



