224 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



be a proteid, since neither peptic nor tryptic digestion 

 destroys it. Numerous " pure " preparations of peroxidase 

 have been made since Slowtzoff's, but without any definite 

 conclusion having been drawn. Among these were those 

 of Bach and Chodat (1903), Tschirch and Stevens (1905), 

 Bach (1908), Bach and Tscherniack (1908), Deleano (1909), 

 Euler and Bolen (1909). The last-named investigators 

 found that the longer their peroxidase from horse-radish 

 was dialyzed, the more active it became, and that its 

 nitrogen content increased, whereas the ash decreased. 

 Bach and Chodat also used horse-radish as the source of 

 their peroxidase. In its purest form this was an amor- 

 phous brownish substance. It contains nitrogen and 

 reducing substances which are not sugars, but gives none 

 of the reactions of protein. On heating with caustic soda 

 ammonia is evolved, also substances having the odour of 

 pyridin bases. Both ammonia and pyrrol are given off 

 when it is heated with metallic potassium. It leaves but 

 little ash, which consists of phosphates of calcium, mag- 

 nesium, sodium, and potassium. Iron and manganese are 

 absent from it. 



COMPOSITION AND PROPERTIES OF TYROSINASE. 



The enzyme tyrosinase occurs in many fungi and in 

 some of the flowering plants. Its action is not specific for 

 tyrosin alone, but includes the oxidation of many related 

 substances. It is differentiated from laccase by the type of 

 substrate upon which it acts, as well as by its greater 

 susceptibility to destruction by heat, alcohol, acids, and 

 alkalies. 



Abderhalden and Guggenheim (1907) showed that T |- - 

 hydrochloric acid entirely stops the action of tyrosinase, 

 but the same concentration of sodium hydroxide exerts 

 only a retarding influence. Since neutralization fails to 



