Relation between Black and Red Melanin Pigments in Feathers

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Abstract
The absorption spectra and solubilities of red and black melanins from feathers of several breeds of domestic fowl and the effects of oxidizing and reducing agents upon these properties were investigated. It was found possible to oxidize black melanin in the direction of red, but even newly formed natural red melanin could not be oxidized to black or black reduced to red. Changes in the absorption spectrum taking place during the oxidation of tyrosine and dopa were also followed and found to proceed first to the black type of spectrum and then to the red with further oxidation. It is concluded that natural red melanins and melanophores probably do not represent transitional stages in the formation of black. An iron-containing component of red melanin obtained from red and buff feathers is described and shown to have characteristics very similar to those of the remainder of the red melanin which contains no iron. The possibility of tyrosinase producing variously colored "melanins" from substrates other than tyrosine is discussed. The irreversible differentiation of melanophores into distinct types might be explained on the basis of known characteristics of the pigment-producing reactions. The beginning of pigment production could "irreversibly" determine the type of cell by stabilizing conditions favorable for the continued production of that type of pigment.