248 Mr. A. Compton. Optimum Temperature of 



Table II. 



Temperatures at the beginning and 

 end of each experiment. 



oalicm hydrolysed. 



o 



per cent. 



17 -8-17 -6 



24 -2 



29 -3-29 5 



42-8 



34 -7 



50-0 



41 -8-41 -7 



43 -0 



50 -2-50 3 



31 -4 



57 -5-57 -6 



16 -4 



Next the activity of the enzyme was determined in the vicinity of + 34° 

 for a 15 hours' action with each of the following concentrations of the 

 substrate: M/5, M/10, M/15, M/30, and M/50, the effect of which on the 

 optimum temperature of the enzyme it was ultimately intended to study. 

 The temperature actually employed was 33-6 -33 - 8° ; and the experimental 

 details were the same, except the dilutions, as already described for the 

 preliminary determination. The numbers obtained are given in Table III. 



Table III. 



Quantity of enzyme. 



Salicin hydrolysed per cent, for the following concentrations : — 



M/5. 



M/10. 



M/15. 



M/30. 



M/50. 



mgrm. 













0-5 





31 -4 



35 -8 



28 -2 





1 -o 



55 1 



57 -5 



58 -5 



49 5 



36 -9 



2-0 



79 -4 



84 -7 



88 -7 



77 -0 





3-0 



88 -3 



93-9 



97-5 



90 -0 



77 -2 



5-0 



94 -2 



97 5 



99 -6 



99 



93-9 



7-0 



94-9 



96 -7 



99 -2 



100-6 



100-0 



10-0 



95 -7 



100 -2 



99 -6 





100 -5 



12 -5 



95 -7 





100-6 



100 6 



100 -o 



These numbers give, on plotting the percentage of salicin hydrolysed 

 against the quantity of enzyme in play, the activity curves shown in fig. 3. 



The influence of the substrate concentration on the optimum temperature 

 of the ferment, the fourth stage of the inquiry, may now be considered. 

 This is the case of determining the optimum temperature in a series of 

 experiments in which the concentration of the enzyme is kept constant while 

 that of the substrate varies. The concentration of the enzyme chosen, in 

 accordance with fig. 3, was 04 mgrm. in 5 cm. 3 , i.e. 8 x 10 -8 grm. per cm. 3 of 

 the reaction mixture. Five different solutions of the enzyme were prepared 



