OXIDASES 391 



the value of the timber,* while the lacquer industry of China 

 and Japan has been built up on the facts relating to the action 

 of the oxidase, laccase, on the expressed sap of species of 

 Rhus. (See below.) 



Oxidases are very widely distributed in the vegetable 

 kingdom ; in the higher plants they may occur in any organ 

 — stem, root, leaf, laticiferous tissue, petals, and fruits. 



Several oxidases have been distinguished, e.g. laccase, 

 which has already been mentioned ; tyrosinase, which oxidizes 

 tyrosine into homogentisinic acid (p. 359) ; olease, from olives, 

 which can oxidize fats into simpler fatty acids, f and others 

 which oxidize sugars into carbon dioxide and water. + 



The action of oxidases may be illustrated by a brief refer- 

 ence to laccase, an enzyme which was first investigated by 

 Yoshida.§ The latex of many species of Rhus rapidly turns 

 brown and finally black on exposure to the atmosphere ; if 

 the juice be evenly spread out, the final product is black and 

 shiny. The extract of the plant contains urushic acid (laccol) 

 which is oxidized into oxyurushic acid : — 



Ci,Hi«0, + = Ci,H,803 



The action takes place best at 20° C. in the presence of mois- 

 ture and oxygen ; at higher temperatures it is destroyed, at 

 63° according to Yoshida, and at 70° according to Bertrand. 

 Bertrand || also has given much attention to this oxidase, and 

 the most important fact ascertained by him in this connexion 

 is that the presence of manganese is all-important. He found 

 that the activity of the ferment is directly proportional to the 

 amount of the metal present, which acts as a co-enzyme (p. 3 5 5). 

 But whether manganese is essential for all oxidase reactions 

 is uncertain, for Bachl! states that he has prepared a tyrosinase 

 which will oxidize tyrosine in the absence of manganese and 

 of iron. 



* Bailey: " Bot. Gaz.," 1910, 50, 142. 

 fTolomei : " Chem. Centrbl.," 1896, i, 879. 

 JSee Palladin : " Zeit. physiol. Chem.," 1906, 47, 407. 

 § Yoshida : " J. Chem. Soc, Lond.," 1883, 43, 472. 



II Bertrand : " Compt. rend.," 1895, 120, 266 ; 1895, 121, 166 ; 1896, 122, 

 1132; 1896, 123, 463; 1897, 124, 1032, 1355. 



ir Bach: " Ber. deut. chem. Gesells.," 1910, 43, 362. 



