1913.] 



Studies on Enzyme Action. 



337 



of M/5 and M strength being almost the same, less change taking place in 

 a solution of 5M strength. When change was complete in the weakest 

 solution, only 1/5 of the urea in the solution of intermediate strength was 

 hydrolysed and about 1/23 of. that in the strongest solution. 



To ascertain the optimum strength of solution, a comparative experiment 

 was made with solutions of M/2 and M strength (the two graphs marked h). 

 Again, the solution of molecular strength was found to be slightly the more 

 active. 



On contrasting tbe behaviour of solutions of molecular and twice molecular 

 strength (the two graphs marked d), it was found that the change took place 

 at very nearly the same rate in each, being slightly more rapid in the weaker 

 during more than half the period of change. 



Two experiments were made with solutions of molecular strength, twice 

 the usual amount of enzyme being added to the one (the two graphs marked a) . 

 these gave results showing that the use of the larger proportion of enzyme 

 is attended with a slight advantage. 



The striking fact brought out in all the graphs representing experiments 

 made in presence of carbonic acid is the approximation of the rate of change 

 to a " linear " character. 



To secure a more rigid comparison, smooth curves were drawn carefully 

 to a large scale from the data obtained in the experiments and the rates of 

 change were deduced by finding the value of the~tangent at each of a series 

 of points. The results are given in Table D. 



It will be noticed that the influence of the acid increases as the action 

 proceeds and that the rates are not far from being constant over con- 



dxldt 



siderable intervals. The values of the ratio — - — in no wav correspond to 



a—x 



those to be expected in the case of a change proceeding at unimolecular 

 rate, which is commonly regarded as the rate to which such actions tend to 

 approximate. 



Hydrogen Cyanide. — In view of the fact that hydrogen cyanide is a product 

 of the hydrolysis of a considerable number of glucosides by " emulsin " and 

 other enzymes, as well as on account of its remarkable physiological 

 activity, it appeared to us to be important to study its behaviour towards 

 an enzyme with which, presumably, it is not ordinarily brought into relation- 

 ship. Our anticipation that it' would act merely as a very weak acid and 

 accelerate hydrolysis was proved to be correct. The results of a series of 

 experiments with various strengths of the cyanide are given in Table E and 

 as graphs in Diagram 16. 



It will be seen that the accelerative influence increases with the 



