1 68 GLUCOSIDES 



whilst the enzyme amygdalase,* contained in yeast, is only 

 able to effect a partial hydrolysis to glucose and mandelo- 

 nitrile glucoside.f . 



CjjoH^NOj! + H 2 = C 6 H 12 6 + C 14 H 17 NO 6 



On the other hand, emulsin can hydrolyse other gluco- 

 sides, besides amygdalin, such as salicin, arbutin, etc. 



THE CONSTITUTION OF THE GLUCOSIDES. 



The constitution of the natural glucosides can be best 

 understood by a brief consideration of the simplest known 

 artificial glucosides which have been synthesized from glucose. 



The 7 lactone formula for glucose (see p. 67) with its 

 asymmetric terminal carbon atom accounts for the ability of 

 glucose to react with methyl alcohol to form two isomeric a- 

 and /3-methyl glucosides J according to the equation : 



O_ 



CH 2 OH CHOH CH CHOH CHOH CHOH + CH 3 OH 



= CH 2 OH CHOH CH CHOH CHOH CH OCH 3 + H 2 O 



The a-glucoside, which is dextro-rotatory, is hydrolysed 

 by maltase, but not by emulsin, while the /3-glucoside, on 

 the contrary, is unaffected by maltase, but is hydrolysed by 

 emulsin. 



As the result of studying the action of these two enzymes 

 upon other glucosides, Fischer divides these substances into 

 two classes known as a-glucosides and /3-glucosides, according 

 as they are hydrolysed by maltase or emulsin respectively. 

 Amygdalin is, therefore, an a- /3-glucoside, since of its two 

 glucose molecules, one is the a- and the other is the /3-modi- 

 fication. 



Since most natural glucosides yield on hydrolysis a sub- 

 stance containing a hydroxyl group, it seems reasonable to 



* Caldwell and Courtauld: " Proc. Roy. Soc., Lond.," B., 1907, 79, 350. 



f Fischer: " Ber. deut. chem. Gesells.," 1899, 28, 1509. 



{ A number of analogous compounds have since been prepared by Fischer 

 and his co-workers from mannose, galactose, and fructose, the resulting com- 

 pounds being termed mannosides, galactosides, and fructosides respectively. 



See also section on Enzymes, p. 355. 



