464 ENZYMES 



Medicago sativa is composed of the calcium salts of glycollic, 

 citric, and malic acids. 



According to Wolff,* moreover, a very dilute ferrocyanide 

 solution mixed with a colloidal iron solution gives all the re- 

 actions of an oxidase and is partly destroyed by boiling or 

 mixture with traces of metallic salts. But the fact that an 

 inorganic complex may bring about the same result as an 

 oxidase, does not militate against the organic structure of 

 naturally occurring oxidases. Finally, as has been mentioned 

 above, peroxidase has been purified to such a degree that the 

 final preparation contained but -06 per cent of iron and showed 

 no decrease in its activity. 



MODE OF ACTION OF ENZYMES. 



To explain the mode of action of inorganic catalysts, it is 

 frequently supposed that they form labile additive compounds 

 with one of the reacting substances which then react more 

 readily than the original substance would have done. 



Similarly, in the case of the enzymes, it is now generally 

 assumed that they enter into some form of loose combination 

 with the substrate ; in spite of this the enzyme is, in general, 

 not altered by the reaction but retains its original activity 

 after having completed its work, unless the products of the 

 reaction have any deleterious effect on it. 



In the group of carbohydrates the action of the enzymes 

 is usually regarded as being more or less specific, each disac- 

 charide being hydrolysed only by its own enzyme, e.g. cane 

 sugar by invertase, milk sugar by lactase, and malt sugar by 

 maltase. 



That this specific activity is in some way connected with 

 the molecular structure of the substances would appear from 

 the researches of Fischer on the action of enzymes upon artifi- 

 cial glucosides. Fischer, by the action of methyl alcohol and 

 hydrochloric acid on glucose, obtained two stereoisomeric 

 methyl glucosides known respectively as the a and j8 variety. 

 Now these two substances differ from each other only by the 

 arrangement in space of the groups attached to the terminal 



* Wolff : " Compt. rend.," 1908, 147, 745. 



