598 SUBSTRATE CONCENTRATION AND HYDROLYSIS 



thereby increases the concentration of active ions. He was able to 

 confirm this by independent measurement of the ion concentration 

 (by means of the conductivities). It follows, as emphasized by 

 Stieglitz, that if the above mechanism is correct so called catalytic 

 reactions are merely limiting cases of ordinary reactions in which the 

 combination of the "catalyst" with the substrate or with the products 

 of hydrolysis is too small to be measured. It seems probable that 

 enzyme reactions are of the same type. There is no doubt, at least, 

 that the enzyme often combines with the products of the reaction 

 and so shifts the equilibrium. Bodenstein and Dietz^^ have shown 

 experimentally that this is true in certain cases. It would seem better, 

 therefore, to consider enzyme reactions as cases of bimolecular reaction 

 in which one of the products dissociates more or less completely with 

 the liberation of active enzyme; if the dissociation is complete the 

 result would be a monomolecular reaction and, if no dissociation 

 whatever takes place, a bimolecular reaction. Most enzyme reactions 

 are apparently intermediate. The specificity of enzyme reaction 

 thus becomes neither more nor less remarkable than the specificity 

 of any other chemical reaction. (The author has had the privilege 

 of discussing the above points with Dr. K. G. Falk who has reached 

 independently similar conclusions.) It was shown in a previous 

 paper^'* that the above conception of enzyme reactions as applied to 

 pepsin gives a quantitative explanation for the kinetics of the reaction 

 and explains the fact that the rate is not always proportional to the 

 total concentration of pepsin. Arrhenius^^ has pointed out that it 

 also gives the explanation of Schlitz's rule and the divergence from 

 the monomolecular law. 



It is clear from the brief account of catalytic reactions given above 

 that the same apparent divergences from the law of mass action are 

 to be found in these reactions as in enzyme reactions and that the 

 divergences in many cases at least are caused by the fact that the 

 active concentration is not the same as the total concentration of 

 substance. It seems quite probable that the same explanation appHes 

 to both. There is no doubt that the saturation theory is sufficient 



^^ Bodenstein and Dietz, Z. Elektrochetn., 1906, xii, 605. 

 ^4 Northrop, J. H., /. Gen. Physiol., 1919-20, ii, 471. 

 ^^ Arrhenius, S., Med. Nohelinst., 1908, i. 



