488 KINETICS OF TRYPSIN DIGESTION 



suggestions of Henri^ and of Brown^ that the law of mass action in 

 its simple form does not hold but that the velocity of the reaction de- 

 pends upon the decomposition of a compound between the enzyme 

 and substrate. There is a large amount of evidence that a compound 

 is first formed in many chemical reactions and it has even been stated 

 (Kekule) that no reaction can take place without an addition com- 

 pound first being formed between the reacting substances. It is 

 quite probable that such a compound is formed in the case of enzyme 

 reactions. The question is whether a sufficient amount of the com- 

 pound is present at any time to make the kinetics of the reaction 

 depend on the concentration of the compound rather than on the 

 concentration of the reacting substances. Henri/ and MichaeHs 

 and Menten^ have attempted to explain the kinetics of invertase 

 hydrolysis by the assumption that the enzyme and substrate combine, 

 according to the law of mass action, to form a compound which sub- 

 sequently decomposes, liberating the free enzyme and the products 

 of the reaction.^ It is also assumed that the velocity of hydrolysis 

 depends on the concentration of this compound. It was pointed 

 out by the writer,' that if the velocity of hydrolysis depended on the 

 amount of compound formed, then the concentration of substrate 

 required to give the maximum velocity of hydrolysis {i.e. to "saturate" 

 the enzyme) should increase with increasing concentrations of enzyme, 

 since it will obviously require more substrate to saturate 100 units 

 of enzyme than it will require to saturate 1 unit. The experiments 

 did not confirm the expectation. It was found that the relative 

 velocity of hydrolysis of different substrate concentrations is always 

 the same, within the experimental error, no matter what enzyme 

 concentration is used (provided the same amount is used with each 

 substrate concentration). It was stated in the article referred to 

 that this was contradictory to the assumption that there was a com- 



" Henri, V., Compt. rend. Acad., 1902, xxxcv, 916; Z. physik. Chem., 1905, li, 19. 



^ Brown, A. J., J. Chem. Soc, 1902, Ixxxi, 373. 



^ Michaelis, L., and Menten, M., Biochem. Z., 1913, xlix, 333. 



^ It has been shown by Simons in Nelson's laboratory that the method used by 

 Michaelis to measure the initial velocity gives values which cannot be used over the 

 entire course of the reaction. 



7 Northrop, J. H., J. Gen. Physiol, 1919-20, ii, 595. 



