412 PROCESSES INFERRED FROM DIRECT OBSERVATION 



In accordance with this view, Knoop has found that if aromatic 

 derivatives of fatty acids containing an even number of carbon atoms 

 be administered to animals, Phenyl-acetic Acid appears in the urine, 

 while if aromatic derivatives of fatty acids containing an odd number of 

 carbon atoms in the molecule be administered, the phenyl-group is 

 split off as Benzole Acid which, as usual, combines with glycocoll in the 

 tissues and appears in the urine as Hippuric Acid. 



OXIDIZING ENZYMES. 



In a variety of animals and plants there are to be found substances 

 which are capable of accelerating certain oxidations. These sub- 

 stances, in the majority of cases, resemble the hydrolyzing enzymes 

 in the minute quantities in which they are effective, and in their insta- 

 bility toward heat. In other cases they are thermostabile and even 

 resist boiling. The discovery of the oxidizing enzymes we owe to the 

 versatile investigator Schonbein (1799-1868), who employed Guaiacum 

 Tincture as a means of detecting them. This substance is tinged blue, 

 a coloration due to oxidative changes, by many tissues and tissue- 

 fluids in the presence of peroxides, such as, for example, Hydrogen 

 Peroxide. It is found, however, that the oxidizing ferments do not by 

 any means act upon all oxidizable substances equally, on the contrary 

 there is a high degree of Specificity in their effects. Thus the enzyme 

 or group of enzymes occurring in the liver and in the spleen which oxi- 

 dizes Purines, converting, for example, Xanthin and Hypoxanthin into 

 Uric Acid, does not attack alcohols, aldehydes or polyphenols. On the 

 other hand the alcohol oxidizing ferment or Alcoholase which oxidizes 

 ethyl alcohol to acetic acid, does not attack purines or polyphenols. 



The best-studied examples of the oxidizing enzymes are those which 

 are afforded by the Laccases, which bring about the hardening of 

 lacquer varnish. A very active enzyme has been prepared from the 

 sap of Rhus succedanea by Bertrand, who coagulates the sap with 

 alcohol, redissolves the coagulum in water, and then recoagulates with 

 alcohol. The coagulum is dried in vacno and is then obtained as a 

 white powder which is readily soluble iu water, and is characterized 

 by its high content of Manganese. The activity of the laccase in oxidiz- 

 ing polyphenols is, in fact, dependent upon the presence of manganese. 

 Thus Bertrand, in studying the action of a similar substance from 

 lucerne with and without the aid of manganous salts, obtained the 

 following results: 



Manganous salt alone . . . . ... . . 0.3 c.c. oxygen absorbed 



Laccase from lucerne, alone ....... 0.2 " " " 



Laccase plus manganous salt 6.3" " " 



We know that in many cases the oxides of polyvalent metals may act 

 as carriers of oxygen, through the intermediate formation of Peroxides 

 which are more active oxidizing agents than free oxygen itself. An 



