COMPOSITIOX OF MELAMX 469 



Fiirth consiilers that iioitlier the .suli)hur nor the iron are indispensa- 

 ble constituents of the melanin. Probably the melanin molecule con- 

 tains at(mi-coinploxes that have a tendency to bind certain sulphur 

 and iron comi)()Uiids (e. g., cystine or hematin derivatives). 



There is much reason to believe that the melanin is derived from 

 certain p:roups of the protein molecule that seem readily to form col- 

 ored compounds. The aromatic compounds of the protein inolecule, 

 such as tyrosine, ]i]ienylalaiiine, and tryptophane, readily condense 

 with elimination of water and absorption of oxygen, to produce dark- 

 colored substances. When proteins are heated in strong hydrochloric 

 acid, we obtain a dark-brown material, which closely resembles the 

 melanins both in elementary composition and in general properties, 

 so that it is referred to as "artificial melanin" or "melanoid sub- 

 stance." These substances, like the natural melanins, when decom- 

 posed by fusing with caustic potash, yield skatole, indole, and pyrrole 

 derivatives, which are undoubtedly derived from the tyrosine and 

 tryptopliane of the protein molecule. Therefore, it seems probable 

 that both the melanoid substances and the true melanins are formed 

 from the chromogen groups of the protein molecule through processes 

 of condensation, elimination of water, and the taking up of oxygen. ^^ 



Tyrosinase. — In the sepia sacs of the cuttle-fish, in meal-worms 

 which form a melanin-like pigment, and in plants that produce the 

 black Japanese lacquer, have been found oxidizing enzymes that have 

 the property of producing black pigment by their action upon tjTO- 

 sine and other aromatic compounds. Neuberg ° found that extracts 

 of a melanosarcoma of the adrenal could produce pigment from 

 epinephrin and ^-oxyphenylethylamine, but not from tyrosine. The 

 ink sacs of the squid contain an enzyme forming a pigment from 

 epinephrin, apparently through oxidation and condensation. These 

 enz^'mes may, therefore, possibly be responsible for the production 

 of melanin in animal tissues, by causing oxidative changes in the 

 chromogen groups of the protein molecule that are liberated by auto- 

 lysis (see "Tyrosinase" p. 73). v. Fiirth urges strongly the view 

 that both normal and pathological melanin formation depend upon 

 the action of the tyrosinase or allied enzymes in conjunction with 

 autolytic enzjones; the latter split free the chromogen groups of the 

 protein molecule, which are then oxidized by the tyrosinase, undergo 

 condensation, and take up sulphur- and iron-holding groups and also 

 other organic compounds, the entire complex forming the melanin. 



Properties of Melanin. — Wlien isolated in a pure condition, 

 melanin is a dark-brown substance of amorphous structure, no mat- 

 ter how black the material from which it is derived may be.^" It is 



SiiSee Herzmark and von Fiirtli, Biochcm. Zeit.. lill."? (40), 130. 



9 Zoit. f. Krebsforsch.. IflO!) (S), 195. 



10 Spiegler, (Hofmeister's Beitr., 1903 (4). 40) claims to have isolated from 

 white wool a white chromogen, closely related to melanin chemically, but Gortner 



