1904.] 



Studies on Enzyme Action. 



535 



with acid — in other words, it must materially increase the magnitude 

 of the active system : this would lead to an increase in the rate of 

 change. 



Any substance having an attraction for water should exercise a 

 similar influence : it is easy to understand that, in the case of milk 

 sugar, as we have shown, the rate of change is as much accelerated by 

 either glucose or galactose as it is by milk sugar and that the neutral 

 salt, potassium chloride, exercises about the same influence as one of 

 these sugars when used in equivalent amount. It is well known that 

 the hydrolysis of cane sugar is hastened by neutral salts,* but it has 

 not been noticed previously that the products of change exercise an 

 accelerating influence. 



Influence of Temperature. — The effect of temperature on the rate at 

 which chemical changes generally take place has been discussed at 

 length by Arrhenius. f Frankly recognising that the rate at which 

 change increases as temperature rises is too great to be ascribed to an 

 increase of the " ionisation " or to a diminution of the viscosity of the 

 solution, Arrhenius has introduced the conception of an active part 

 or mass but without in any way defining the nature of this mass. In 

 applying this conception specially to the hydrolysis of cane sugar, 

 he assumes that the formation of the active mass involves an absorp- 

 tion of heat, and, further, that although it is present in very small 

 proportion relatively to the total sugar, the proportion increases 

 rapidly as the temperature rises. Adopting the ordinary convention 

 he supposes that the active mass undergoes hydrolysis at the expense 

 of the hydrogen ions of the acid, at a rate, however, that is almost 

 independent of the temperature. Availing himself of the equation 

 which van't Hoff had put forward to express the alteration of 

 equilibrium with temperature in the case of reversible interactions, he 

 deduced the expression 



q Tt-To 

 K tl = K< . 6 2 ' TjTo , 



where K t} and K tn are the velocities at two temperatures and q is the 

 heat absorbed in the formation of the active mass— this being an 

 expression from which it is apparent that a rise in temperature should 

 favour the formation of the active mass and vice versa. Arrhenius 

 applied this expression to a large number of simple chemical changes, 

 especially to cases of hydrolysis, for which the rate had been measured, 

 and showed that it was in agreement with experimental facts. 



The idea of an active mass was extended to explain the influence of 

 salts : it was arbitrarily assumed by Arrhenius that these increased 

 the proportion of the active mass, notwithstanding that they decreased 

 the number of hydrogen ions. 



* Spohr, ' Zeit. Phys. Chem.,' 1888, vol. 2, p. 194. 

 f « Zeit. Phys. Chem.,' 1889, vol. 4, p. 226. ' 



