246 Mr. A. Compton. Optimum Temperature of 



The successive stages in the inquiry may be briefly summarised as follows : 

 (1) a preliminary determination of the activity of the specimen under certain 

 chosen conditions as regards the concentration of the substrate, the tem- 

 perature, and the duration of the experiment ; (2) a preliminary determina- 

 tion of the optimum temperature with the quantity of enzyme found 

 capable of producing 50 per cent, hydrolysis of the substrate under the above 

 conditions ; (3) a determination of the activity curves of the enzyme at the 

 temperature thus found, in an action of the same duration for five concentra- 

 tions of the substrate M/5, M/10, M/15, M/30, and M/50 ; (4) a determina- 

 tion of the optimum temperature of the enzyme for each of the five 

 concentrations of the substrate in presence of a constant enzyme concentra- 

 tion ; (5) a determination of the optimum temperature of the enzyme for 

 each of the five concentrations of the substrate with quantities of enzyme 

 indicated by the activity curves as capable of producing 70 per cent, 

 hydrolysis of the substrate in the given time : (6) a determination of the 

 optimum temperature of the enzyme for a constant concentration of the 

 substrate in presence of different enzyme concentrations. 



The preliminary determination of the activity of the enzyme was carried 

 out in a M/5 dilution of the substrate during a period of 15 hours at 40°. 

 The practical details were as follows : 286 mgrm. of salicin and varying 

 quantities of the enzyme dissolved in 5 cm. 3 of water, specially purified by 

 redistillation under diminished pressure, were introduced into each of a 

 series of seven clean Jena glass test-tubes. The tubes were incubated for 

 15 hours in a water thermostat at 40°, after which the enzyme action was 

 stopped by rapidly cooling the tubes aud then adding to each a drop of 

 concentrated solution of ammonium hydroxide. The proportion of glucoside 

 hydrolysed in each tube was estimated by the increase of reducing power, 

 measured by the method of Bertrand.* The numbers obtained are set out in 

 Table I. 



Table I. 



Quantity of enzyme. 



Salicin hydrolysed. 



mgrm. 



per cent. 



0-6 



34 -8 



1 5 



67 "2 



3 -0 



86 -8 



4-5 



91 -2 



6 



91 -7 



7-0 



96 -1 



9 



97 -0 



* ' Bull. Soc. Chim.' [3], 1906, vol. 35, p. 1285. 



