1904.] 



Studies on Enzyme Action. 



533 



It will be seen that the value of the temperature constant for milk 

 sugar is nearly half as great again as that for cane sugar. 



That temperature changes have a similar effect on the hydrolysis of 

 milk sugar by sulphuric acid is shown by the following figures, obtained 

 by hydrolysing a 0*5 gramme-molecular proportion solution of the 

 sugar by means of 0*25 gramme-molecular proportion acid. 



Lastly, the effect of adding a 0*5 gramme-molecular proportion of 

 potassium chloride at the two temperatures was determined ; it will be 

 seen that this salt has a considerably greater accelerating influence at 

 the higher temperature. 



It is to be noted that maltose (K = 4*49) and milk sugar (K = 3*53) 

 are hydrolysed at similar rates at 60° *1 ; as the rate of hydrolysis is 

 affected to different extents by a rise of temperature in the two cases, 

 there will be a temperature at which the two should be hydrolysed at 

 the same rate; and above this temperature milk sugar should be hydro- 

 lysed more rapidly than maltose. The temperature at which the two 

 sugars should behave alike, deduced from Arrhenius's equation, is about 

 77° ; we intend comparing the hydrolysis of the two sugars at this 

 temperature. 



Theory of Hydrolysis by Acids. — When the action of enzymes on the 

 sugars is contrasted with that of acids, the enormous difference in the 

 rates at which enzyme and acid effect hydrolysis is very striking ; thus, 

 whereas an extract of lactase prepared as described on pp. 503 to 504, 

 to which sufficient milk sugar has been added to give a 5-per-cent. solu- 

 tion, will hydrolyse about one-fourth of the sugar at 35° in about an 

 hour, it takes twice normal hydrogen chloride at the same temperature 

 about 5 weeks to effect the same amount of hydrolysis.* 



Nevertheless, a very simple explanation of the action of acids may 

 be given if the problem be considered from a point of view similar to 

 that applied to enzyme action. In the first place, it may be assumed 

 that an active system is formed by the combination of a part of the 

 sugar with a part of the acid • and as the water molecules in the solu- 



* Although no information is at present forthcoming admitting of a definite 

 conclusion, it cannot be doubted that the amount of enzyme made use of in 

 hydrolysing sugars, regarded as a molecular proportion, must be extraordinarily 

 small. Any such conclusion as this makes their action appear all the more 

 remarkable. 



Temperature. 



60°T 

 74°-l 



K. 



3-36 

 22-5 



K with KC1. 

 3-79 

 29-0 



K without KCL 

 3-53 

 25-05 



2 P 2 



