THE PLANT OXIDASES 225 



restore the former activity of the enzyme, it is clear that 

 it has been destroyed by the reagent, and not merely 

 inactivated. 



As a general rule, tyrosinase is found wherever laccase 

 is, but the converse of this is not true. 



Bertrand and Mutermilch (1907) prepared it from bran 

 by precipitation of an aqueous extract with alcohol in 

 certain proportions. The substance so obtained was free 

 from laccase. It is soluble in water, and may be filtered 

 through a Chamberland filter to yield a clear solution 

 which does not darken when exposed to the air. The 

 addition of tyrosin results in the production of a rose 

 colour, altering to red and then brownish-black. 



It was ascertained by Bach (1908, 1) that tyrosinase, 

 like laccase, consists of a peroxidase and a peroxide. For 

 whereas the addition of hydrogen peroxide to an active 

 solution prepared from sound fungal tissue did not increase 

 its activity, yet when a decomposing tissue was the source 

 of enzyme, and the tyrosinase action was not vigorous, a 

 marked increase resulted from the addition of a little very 

 dilute hydrogen peroxide. That the naturally occurring 

 peroxide can thus be replaced shows that the specific action 

 of the enzyme is due to the peroxidase. 



In order to illustrate the effect of added hydrogen 

 peroxide just mentioned, it may not be amiss to quote the 

 figures obtained by Bach in his experiment. Aqueous 

 extracts of tyrosinase were made from young unblemished, 

 older slightly damaged, and from putrid specimens of 

 Russula delica. These are solutions I., II., and III., 

 respectively. Of each extract, diluted ten times with 

 water, 10 c.c. was taken and mixed with 10 c.c. of a solu- 

 tion containing 0-05 per cent, tyrosin and 0-04 per cent, 

 sodium carbonate. To this 30 c.c. of water was added, 

 and after standing for twenty-four hours it was titrated 



15 



