JOHN H. NORTHROP 497 



tional to the relative amount of trypsin taken, i.e., if Eo is the value used when 

 1 cc. of trypsin is taken then nEo will be the value for n cc. 



K' is determined by substituting the values of C, E, and S and solving for K\ 

 It is, therefore, a second arbitrary constant. 



Table V shows that the calculated and observed values are con- 

 cordant. It also shows that the relative rate of hydrolysis of any 

 two gelatin concentrations with any one trypsin concentration is 

 independent of the value of this trypsin concentration. 



The results when the enzyme or substrate concentrations are varied, 

 therefore, agree with those predicted by the assumption that the 

 enzyme and gelatin combine to form a compound and that the rate 

 of hydrolysis is proportional to the concentration of this compound. 



The equation which was used to calculate these values, however, 

 contains two arbitrary constants and is of a form to fit any curve which 

 at first shows direct proportionality and then approaches a maxi- 

 mum value. It is not surprising, therefore, that the calculated and 

 observed results agree. The test of an equation of this type is to see 

 whether or not it will fit the results of an experiment other than the 

 one from which the values of the constants was originally obtained. 

 As will be seen below, this is not the case; the equation breaks down 

 when the experiment is performed in the presence of inhibiting 

 substances. 



Influence of the Gelatin Concentration on the Retarding Effect of 

 Inhibiting Substances. 



It was found^ in studying the influence of the inhibiting substance 

 on the rate of digestion that the experiments agreed with the assump- 

 tion that the enzyme and inhibitor combined to form a compound 

 that was inactive and that the rate of hydrolysis was proportional 

 to the concentration of free enzyme. It was also found that there 

 was direct evidence that the inhibitor affects the enzyme and not the 

 substrate. The experiment summarized in Table V, however, if 

 taken alone, shows that the influence of the substrate concentration 

 agrees with the assumption that the rate of hydrolysis is proportional 

 to the amount of enzyme combined with the substrate. It is evident 

 that both assumptions cannot be correct. 



