502 ENZYMES 



a hydroquinone substrate which on oxidation gives /)-quinone, 

 a compound that is unable to blue guaiacum. 



According to Ewart * there is no real distinction between 

 oxidases and peroxidases other than a difference in strength. 



A technical application of oxidases is furnished by laccase, 

 an enzyme which was first investigated by Yoshida,t and 

 was employed in China and Japan in the making of lacquered 

 articles. 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 — 



C^HisO, + O = Ci,H„03 



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 con- 

 nection is that the presence of manganese is all-important. 

 He found that the activity of the ferment is directly propor- 

 tional to the amount of the metal present. But whether 

 manganese is essential for all oxidase reactions is uncertain. 



Isolation of Oxidases. 



The isolation of oxidase may be a difficult matter when it 

 exists in a tissue together with its substrate and other enzymes. 

 Bourquelot and Bertrand give the following method for Fungi 

 such as Russula. The tissue is chopped up, extracted with 

 water — which may be warmed — and filtered as quickly as may 

 be. The filtrate is then poured into an excess of strong 

 alcohol, whereby the enzyme is precipitated. The precipitate 

 is then filtered off and dissolved in water. 



* Ewart: " British Assoc. Rep.," 191 5. See also Moore and Whitley : 

 " Biochem. Journ.," 1909. 4» 136- 



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



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

 122, 1132; 1896, 123, 463; 1897, 124, 1032, 1355. See also Rippel : 

 " Biochem. Zeit.," 1923, 140, 315. 



