472 EFFECT OF ENZYME ON DIGESTION OF PROTEINS 



It was suggested by Brown^ that these divergences in the case of 

 invertase were due to the fact that the enzyme formed an intermediate 

 compound with the substrate ; and several formulas'* which fit the ex- 

 perimental facts fairly well have been derived on this assumption. 

 They all contain several arbitrary constants, however, and in the lack 

 of any direct evidence in favor of the mechanism which they assume 

 the agreement between calculated and observed values can hardly 

 be considered conclusive. It is assumed in attempting to explain 

 the mechanism of enzyme reactions from the point of view outlined 

 above, that all the enzyme and all the substrate molecules present 

 are equally able to take part in the reaction; in other words, that the 

 active concentration and total concentration of enzyme (or substrate) 

 are the same or directly porportional to each other. It is obvious 

 that, if the active concentration of substrate or enzyme was not equal 

 to the total concentration, the law of mass action would fail to hold 

 if the total concentrations were used in formulas derived from this 

 law, since the law itself states only that the rate of reaction is propor- 

 tional to the active concentration of the reacting substances. It 

 appears a priori quite possible that active enzyme or substrate mole- 

 cules may exist in solution in equilibrium with other molecules which 

 do not take part in the reaction. The concentration of active enzyme 

 molecules (in the sense of the law of mass action, i.e. those which 

 take part in the reaction) would then be some other function of the 

 total concentration and would not be directly proportional to it. 

 The rate of reaction would then also be found to vary as some other 

 function of the total enzyme concentration and not in direct propor- 

 tion to it. An exactly analogous case is well known in general chem- 

 istry; namely, acid hydrolysis." The hydrogen ion is the active part 



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



" Van Slyke, D. D., and CuUen, G. E., /. Biol. Chem., 1914, xix, 146. These 

 authors review the various other formulas proposed. See also Moore, B., in Hill, 

 L., Recent advances in physiology and biochemistry, New York and London, 

 1906, 43. 



^ For a general discussion of this question see Stieglitz, J., and collaborators, 

 Am. Chem. J., 1908, xxxix, 29, 166, 402, 650. Stieglitz's experiments were made 

 on the hydrolysis of esters. These solutions can hardly be considered heteroge- 

 neous and yet show the same divergences from the simple mass action law as do 

 enzyme reactions. This question will be discussed more fully in a subsequent 

 paper. 



