THE NATURE OF ENZYME ACTION 287 



recent work on the synthetic action of enzymes. It will be 

 noticed that, in the list of cases given above, isolactose and not 

 lactose is stated to be formed by the action of lactase on glucose 

 and galactose. Accordingly, the sugar synthesised by the enzyme 

 is not the one which it hydrolyses, but the optical isomer 

 of the latter. Similarly, Croft Hill found that maltose is only 

 produced in small amount by the action of maltase on glucose, 

 and that a new disaccharide (revertose) makes its appearance. 

 Frankland Armstrong states that this revertose is identical 

 with isomaltose, as Emmerling had also concluded. Frankland 

 Armstrong is, indeed, of the opinion that the rule is that 

 with a particular enzyme that body is synthesised which is 

 incapable of being hydrolysed back by the enzyme in question. 



It will be obvious that this conception involves many diffi- 

 culties. To follow the evidence on which it rests, and which 

 consists in the mode of action of maltase and emulsin respectively 

 on glucose, a brief explanation of the stereochemical relations 

 of the glucosides is necessary. Glucose itself is now looked 

 upon as having the structure of a glucoside — i.e. the internal 

 anhydride structure of a lactone. It therefore exists in two 

 optically isomeric forms known as a- and /3-glucose. In water 

 these two forms, which differ in their rotatory power, exist 

 together in equilibrium; according to Tanret, in 10 per cent, 

 solution there is 37 per cent, of the a-form and &$ per cent, of 

 the /3-form. When a solution of glucose in methyl-alcohol, in 

 which also it exists in both a and /3 forms, is acted on by hydro- 

 chloric acid, two stereo-isomeric methyl-glucosides are formed, 

 corresponding to the a- and /3-glucoses. Of these the a-com- 

 pound alone is hydrolysed by the maltase of yeast, and the 

 ^-compound alone by emulsin — the enzyme found so frequently 

 in the higher plants, and which hydrolyses so many of the 

 natural glucosides, such as amygdalin. These latter, then, 

 naturally must be regarded as /3-glucosides, while maltose 

 (glucose-glucoside) is an a-glucoside ; isomaltose is presumably 

 the glucose-/3-glucoside. 



If we take a solution of glucose, therefore, and act upon it 

 by maltose, we should expect, from all that we know of rever- 

 sible reactions, that a certain amount of maltose would be 

 synthesised; and this, in fact, is what Croft Hill originally 

 believed to take place. Later he found that only a small part 

 of the bi-hexose consisted of maltose, the remainder being, as 



