350 ENZYMES 



proteins although it contains no phosphorus ; on the other hand, 

 the purest forms of invertase hitherto obtained contain but 

 little nitrogen and do not give the biuret reaction ; they are 

 rich, however, in carbohydrate and contain organically com- 

 bined phosphorus. 



Considerable difference of opinion exists in regard to the 

 special class of enzyme known as oxidases. These, accord- 

 ing to some authors, as for example Dony-Henault,* are not 

 organic compounds at all, but owe their action to the 

 presence of certain inorganic salts, more especially manganese 

 salts, in colloidal solution. Bertrand,f on the other hand, 

 considers that the laccase of Rhiis succedanea is a protein, 

 whilst Euler and Bolin :J: are of the opinion that the laccase of 

 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. 



PROPERTIES OF ENZYMES. 



A peculiar property of enzymes, in which they differ from 

 inorganic catalysts, is their sensitiveness to heat and light. 



All enzymes are destroyed at ioo° and most of them can- 

 not, with safety, be heated much above 6o°. The statement 

 made by van't Hoff that the velocity of a reaction is doubled 

 for every io° rise of temperature is found to hold good for 

 enzymes also with this reservation, that as the temperature 

 approaches a certain height it begins to have a deleterious 

 effect upon the enzyme ; the so-called optimum temperature 

 for the activity of any particular enzyme is therefore a com- 

 promise between the maximum acceleration effect, which can 

 be attained in accordance with van't Hoff's rule, and the 

 maximum temperature to which the enzyme can be heated 

 without undergoing destruction. Inasmuch as the enzymes 

 themselves are not living — unless, indeed, we consider the 

 phenomena of life to be due to the activities of a complex of 



* Dony-Henault : "Bull. Acad. Roy. Belg.," igoS, 105. 

 + Bertrand ; " Ann. Chim. Phys.," 1907, [7], 12. 

 % Euler and Bolin : " Zeit. physiol. chem.," igog, 61, i. 

 § Wolff : " Compt. rend.,'" 1908, 147, 745. 



