MELANIN 395 



enzymes that have the property of producing black pigment by 

 their action upon tyrosin and other aromatic compounds. These 

 enzymes may, therefore, possibly be responsible for the produc- 

 tion of melanin in animal tissues, by causing oxidative changes 

 in the chromogen groups of the proteid molecule that are 

 liberated by autolysis (see "Tyrosinase " p. 79). v. Fiirth urges 

 strongly the view that both normal and pathological melanin 

 formation depends upon the action of tyrosinase or allied enzymes 

 in conjunction with autolytic enzymes ; the latter split free the 

 chromogen groups of the proteid molecule, which are then oxi- 

 dized by the tyrosinase, undergo condensation, and take up sul- 

 phur- and iron-holding groups and also other organic compounds, 

 the entire complex forming the melanin. 



Properties of Melanin. When isolated in a pure con- 

 dition, melanin is a dark-brown substance of amorphous struc- 

 ture, no matter how black the material from which it is derived 

 may be. 1 It is quite insoluble in all ordinary reagents except 

 alkalies, in which some melanins dissolve easily, and some with 

 difficulty. Strong boiling hydrochloric acid scarcely affects 

 melanin. By the action of sunlight or oxidizing agents on 

 melanin-containing sections the pigment can be bleached out. 

 The chief decomposition-products formed on fusing with alka- 

 lies are indol, skatol, and " melanic acid " ; no cystin, leucin, 

 tyrosin, or other amino-acids can be isolated. Most authors, 

 therefore, consider the melanins as heterocyclic compounds 

 standing in some relation to the indol nucleus. 



If melanin is injected subcutaneously into animals (rabbits and 

 guinea-pigs), there appears in the urine a substance which turns 

 dark brown after the urine has stood for some time (Robert, 

 Helman). The pigment is apparently reduced, particularly by 

 the liver, to a colorless melanogen, which is eliminated in the 

 urine. The same process occurs when melanin is produced in 

 excess and enters the blood, as in the case of melanosarcoma, a 

 colorless melanogen being formed which is excreted in the 

 urine, constituting " melanuria." Occasionally the urine is 

 dark when first passed, because of the presence of melanin, but 

 usually it must be subjected to oxidizing agencies (bromine 

 water, nitric acid, hypochlorites, etc.), or exposed to air to 

 bring out the brown color. Helman 2 says that true melanogen 

 may be considered to be present in urine: (1) If the careful 



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

 white chromogen, closely related to melanin chemically, which causes the 

 white color of wool and hair. 



2 Cent. f. inn. Med., 1902 (23), 1017; Arch, internat. Pharmakodynam., 

 1903 (12), 271. 



