1904] 



Studies on Enzyme Action. 



521 



the hexosides* which undergo hydrolysis under the influence of that 

 enzyme. 



A more absolute proof of the close correlation in configuration 

 between enzyme and hydrolyte cannot well be imagined : it is difficult 

 to interpret such behaviour in any other way than as evidence that 

 the enzyme combines with the hexose in some special, peculiarly intimate 

 manner and is thereby withdrawn from the sphere of action. The 

 retardation cannot well be due to reversion, as in the case of milk 

 sugar the retardation is effected chiefly by glucose when emulsin is the 

 active agent but by galactose alone when lactase is used to effect 

 hydrolysis. 



Emil Fischer's researches have brought to light the remarkable fact 

 that the naturally occurring hexoses or derivatives of these, i.e., glucose, 

 mannose, galactose and fructose, are the only compounds affected 

 either by the organisms which condition alcoholic fermentation or by 

 any of the sucroclastic enzymes. The stereoisomeric hexoses produced 

 by artificial means cannot be fermented ; this is true also of the 

 "lower " and "higher" sugars, whether derived from natural products 

 (arabinose, xylose, etc.) or prepared artificially from the natural 

 products by reducing or adding to the number of carbon atoms in the 

 chain. The fact that resistant materials such as straw, the gums, etc., 

 are pentose derivatives is of interest in this latter connection. Three 

 of the four hexose sugars referred to are fermented readily and 

 apparently with equal ease ; the fourth, galactose, is only slowly 

 fermented : such being the case, it is noteworthy that the formulae 

 ordinarily assigned to glucose, mannose and fructose are reducible to 

 one common enolic form. It is conceivable that this enolic form is 

 the substance actually fermented to carbon dioxide and alcohol. 



CHO 

 HC.OH 

 HO.CH 

 HC.OH 

 HC.OH 



CHO 

 HO.C.H 

 HO.C.H 

 HC.OH 

 HC.OH 



CH 2 .OH 

 CO 



CH.OH 

 C.OH 



HO.CH 



HO.CH 



CH 2 .OH 



CH 2 .OH 



HC.OH 

 HC.OH 



CH 2 .OH 



HC.OH 

 HC.OH 

 CH 2 .OH 



Glucose. 



Mannose. 



Fructose. 



Enolic form. 



* The term " hexoside " is used as a general expression to include all compounds 

 of a glucosidic character derived from a hexose. 



