Issued November 8, 1909. 



United States Department of Agriculture, 



BUREAU OF CHEMISTRY Circular No. 47. 

 H. W. WILEY, Chief of Bureau. 



THE HYDROLYSIS OF SALICIN BY THE ENZYM EMULSIN. 



By C. S. HUDSON and H. S. PAINE, 



Assistant Chemists. 



INTRODUCTION. 



Salicin is a glucosid which occurs in many trees, particularly those 

 of the willow family. In aqueous solution it is hydrolyzed by strong 

 acids to glucose and salicyl alcohol according to the equation of 

 Piria: a C 13 H 18 O 7 + H 2 O = C 6 H 12 O 6 + C 7 H 8 O 2 (salicin + water = glucose + 

 salicyl alcohol). 



It has been found by A. A. Noyes and Hall 6 that the rate of this 

 acid hydrolysis follows the law of unimolecular reactions. The same 

 hydrolysis can also be accomplished by adding to the salicin solution 

 a little of the enzym of almonds, called emulsin, but in this case it has 

 been stated by Henri c and other investigators that the rate does not 

 follow at all the unimolecular law. This statement that the enzy- 

 motic hydrolysis of salicin by emulsin does not follow the usual laws 

 of chemical dynamics has passed unchallenged for many years and has 

 been widely accepted as correct. In confutation of this view, it is to 

 be said that the glucose which is liberated from salicin by the action 

 of emulsin is doubtless /?-glucose, because emulsin hydrolyzes only the 

 /?-glucosids, and /?-glucose has a rotary power of 20; but Henri in his 

 work assumed that the glucose had its usual specific rotation of 52. 

 His polariscopic measurements of the rate of the enzymotic hydrolysis 

 are accordingly incorrect, for he made no correction for the muta- 

 rotation of glucose. In the hydrolysis by acids as studied by A. A. 

 Noyes and Hall this second reaction, the mutarotation of glucose, 

 does not affect the estimation of the extent of the hydrolysis from the 



oLiebig, Ann. Chem., 1845, 56: 35. 

 &Zts. physikal. Chem., 1895, 18: 240. 

 c Lois gne"rales de 1'action des diastases, i). 102. 

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