596 SUBSTRATE CONCENTRATION AND HYDROLYSIS 



showed that an equation might be derived on the assumption of the 

 above mechanism, based on the law of mass action. The validity 

 of this derivation has, however, been questioned by Falk.* Bayliss* 

 has advocated the view that the combination is due to adsorption 

 and cannot be considered a mass action phenomenon. He states, 

 as do Armstrong and Armstrong,^ that the fact that the rate of hydrol- 

 ysis in many cases is nearly independent of the total substrate con- 

 centration cannot be explained on the law of mass action, and must 

 be due to some saturation effect of the enzyme with the substrate. 



The fact is frequently overlooked that purely chemical catalysis 

 in strictly homogeneous solutions also shows apparent divergences 

 from the mass law. This point is, however, discussed by Bredig,' 

 Mellor,^ Lewis,^ and especially by Falk.^'' In the hydrolysis of cane 

 sugar by acids, for instance, the rate of hydrolysis is not proportional 

 to the total concentration of acid used but to the hydrogen ion con- 

 centration. As is well known, the hydrogen ion concentration in 

 heavily "buffered" solutions is almost independent of the total acid 

 concentration in certain ranges so that the hydrolysis of cane sugar 

 by such a solution would show an analogous behavior to enzyme 

 reactions in that the rate of hydrolysis of the sugar would be nearly 

 independent of the total acid concentration. The apparent discrep- 

 ancy of the mass law is therefore due to the fact that the "active 

 concentration" (on which the mass law is based) is in many cases 

 not identical with the total concentration. There is a further discrep- 

 ancy in these cases due to the fact that the rate of hydrolysis in certain 

 concentrations is not proportional to the Ch as determined by the 

 conductivity ratio. This is the so called salt effect and is probably 



4 Falk, K. G., J. Biol. Chem., 1916-17, xxviu, 389. 



^ BayKss, W. M., The nature of enzyme action. Monograph on Biochemistry, 

 London, New York, Bombay, and Calcutta, 3rd edition, 1914. 



^Armstrong, E. F., and Armstrong, H. F., Proc. Roy. Soc. London, Series B, 

 1913, Ixxxvi, 561. 



^ Bredig, G., Ergebn. Physiol., lie AbL, 1902, i, 134. 



^ Mellor, J. W., Chemical statics and dynamics, London, 1904. 



^ Lewis, W. C. McC, A system of physical chemistry, London, New York, 

 Bombay, Calcutta, and Madras, 1919, i. 

 i«Falk, K. G., (in press). 



