29 



fungus, they turned their attention to the case of Russula spp., 

 especially R. nigricans, the color change of which upon injury is 

 from pink or reddish to black. In different researches they 

 showed that laccase could not produce the same effect, and 

 further, that it was an oxidation of a definite chemical substance 

 in the fungus. Bertrand^'' next showed that the crystalline chro- 

 mogen in Russula spp. was tyrosin and that it was also present 

 in beets, potatoes, etc.; accordingly he named the enzyme which 

 Caused this change "tyrosinase," and said that laccase and tyro- 

 sinase were two representatives of the group of "oxidases." 

 About this time it was found that rosettes of tyrosin crystals 

 were present in the tissues of the fungus Russula nigricans. 



At first it was thought that tyrosinase was as wade-spread an 

 enzyme as laccase, but later results show this to be unlikely. 

 Lehman and Sano^^ examined bacteria and higher plants for 

 tyrosinase. A few species of bacteria showed the presence of 

 tyrosinase, but in no case could it be separated from the living 

 bacterial cells. Among the higher plants tyrosinase is present 

 in wheat, barley, potatoes, Papaver orientale, Rhus spp., etc. 

 Thus we see, this enzyme is probably concerned in the formation 

 of the black wound-covering over injured areas on potatoes. 



The action of tyrosinase results in a yellowish pink coloration, 

 then reddish, then brown, and finally black. This reddish black 

 oxidation or condensation product is called melanin and is closely 

 related to the natural animal pigments in dark hair, etc., and 

 also in the so-called melanotic tumors. This action of tyrosinase 

 and the resulting melanin have attracted a great deal of attention. 

 The first investigators said that the action of the tyrosinase was 

 simply the oxidation of tyrosin to melanin, and that the produc- 

 tion of a black coloration in a plant was due to the action of its 

 tyrosinase on tyrosin. However, it soon became clear that the 

 matter was not so simple as at first thought. Certain experiment^ 

 seem to show that the early change of tyrosin to a pink color 



'" Bertrand. Sur une nouvelle oxydase ou ferment soluble oxydant d'origine 

 vegetale. Compt. Rend. Acad. Sci. 122: 1215. 1896. Also Bull. Soc. Chim. 

 [3]. 15: 793- 1896. 



^1 Lehman and Sano. Ueber das Vorkommen von Oxydations-fermenten bei 

 Bakterien und hoheren Pflanzen. Arch. f. Hyg. 67: 99. 1908. 



