No. 540] 



STUDIES ON MELANIN 



753 



in the high percentage of alcohol which was used both 

 to extract the enzyme, and as a solvent. 



The Isolation of a Tyrosinase.— Phisalix (1905), De- 

 witz (1902), Eoques (1909) and Durham (1904), as well 

 as myself (1910 b.) (1911), have shown that the produc- 

 tion of melanin is caused by the action of an oxidizing 

 enzyme of the tyrosinase type upon some oxidizable 

 chromogen, which may, in some instances, be tyrosin. 

 My first step was, therefore, to ascertain whether or not 

 tyrosinase were present in the potato beetle. I found 

 that it was present in large amounts in the beetles that 

 were collected in the field. In order to make sure that 

 there was no mistake, I tested some of the potato leaves, 

 and there I found abundance of tyrosinase. I found, 

 however, that if I removed large larvae to the laboratory 

 and kept them without food until they pupated, that the 

 body contents of these three or four days old pupae gave 

 no test for the enzyme. As a final precaution, however, 

 I used only the unpigmented elytra of beetles which had 

 transformed from such pupa?. In this manner there 

 seems to be no possibility that the food could have con- 

 taminated the material, for a period of a least twelve 

 days without food must have elapsed between the se- 

 curing of the larvae and the removing of the unpig- 

 mented elytra from the adult beetles. The elytra, which 

 showed only a faint trace of the color pattern which was 

 to develop, were ground with quartz sand in an agate 

 mortar, and the mixture leached with distilled water con- 

 taining a few drops of chloroform. The filtered solution 

 was clear, gave an intense blue with a drop of tincture of 

 gum guaiac, produced a rapid darkening in solutions of 

 tyrosin, leading to the deposition of the typical black pre- 

 cipitate, lost its activity at 70°, or in the presence of meta 

 di phenols [see Gortner (1911 b.)], and behaved in every 

 way identically like other preparations of tyrosinase 

 which I have reported from other sources. There can be 

 no doubt that if the pigmentation in other instances is 



