Pheomelanin, the red-brown polymeric pigment in the skin and hair of red-headed humans, is composed of a protein fraction covalently bound to a colored chromophore. Photolysis of aerated aqueous pheomelanin solutions, isolated from human red hair, results in destruction of the chromophore and liberation of the peptide fraction. The rate of photolysis depends on the pH and the concentration of both pigment and oxygen and is slightly inhibited by the enzyme superoxide dismutase (superoxide:superoxide oxidoreductase EC 1.15.1.1). Pheomelanin photolyzed in the presence of nitroblue tetrazolium results in the formation of a blue diformazan, whether or not oxygen is present. Superoxide dismutase inhibits the aerobic photoreduction of nitroblue tetrazolium whereas, in the absence of oxygen, no inhibition is observed. These experiments strongly suggest the involvement of superoxide in the aerobic photolysis of pheomelanin and point out a possible mechanism for ultraviolet-induced cell damage in redheads. The black or brown eumelanins of human skin afford protection against the damaging effects of the ultraviolet component in sunlight (1)(2)(3)(4). Light of these wavelengths, 280-380 nm, is nondestructive to eumelanin and produces reversible changes that are believed to function as mechanisms in this pigment's photoprotective ability. Two such reversible reactions are (i) immediate pigment darkening (3,5,6), an apparent oxidation-reduction reaction resulting in the darkening of preformed pigment, and (ii) an increase in the number and a change in the nature of the unpaired electrons in the pigment (7-9).Fair-skinned humans exhibit a number of abnormal reactions to sunlight, including freckling (10) and a high susceptibility to skin cancer (11)(12)(13)(14). These have usually been attributed to the fact that the skin of these people has a poor tanning capacity, sunburns readily, and contains little pigment. Although pheomelanin, the red-brown or yellow pigment found in the hair of fair-skinned humans (15,16), has yet to be isolated from human skin, there is an increasing amount of indirect evidence that it occurs in melanosomes found in various parts of the body, including the skin (17-22). Pheomelanin is readily photodegraded under physiologically relevant conditions (23, 24), an observation that has led us to suggest the following four mechanisms by which ultraviolet light may deleteriously affect cells containing this pigment: (i) loss of a pigment purportedly responsible for photoprotection; (ii) formation of dermatitic or carcinogenic photoproducts; (Mii) formation of dermatitic or carcinogenic compounds by reactions of photochemically produced intermediates with normal cell constituents; and (iv) formation of photoproducts that inhibit the enzymatic systems responsible for repair of ultraviolet-induced damage. In this paper we support the viability of mechanism iii by presenting evidence that a highly reactive intermediate is formed during the course of the photolysis.The publication costs of this article we...

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Abstract— The action spectrum for superoxide production from aerated aqueous solutions of pheomela‐nin was determined by utilizing the nitroblue tetrazolium‐superoxide dismutase assay for superoxide. Superoxide production was greatest in the UVC regions, but continued well into the visible wavelengths. The marked increase in superoxide production noted in the UVC‐UVB regions of the spectrum suggests that superoxide production may be involved in a number of actinic disorders in fair‐skinned humans.

Melanin isolated from the ink sac of Sepia officinalis (Sepia melanin) has been proposed as a standard for natural eumelanin. There are no standard methods for the isolation, purification, and storage of melanins. Mild methods designed to preserve the native composition and structure of melanin are needed. The specific aim of the present work, using Sepia melanin, was to develop a mild and generally applicable protocol for the isolation and purification of melanins. It is well established that melanin polymers contain a large number of free carboxylic acid residues. These anionic residues are responsible for the cation exchange properties observed for melanins. Heating melanins with hydrochloric acid at reflux has been demonstrated to lead to extensive decarboxylation. Indeed, heat alone has been shown to cause decarboxylation, and care must be exercised to avoid such conditions. By analogy with cation exchange resins, melanins should be isolated and named according to the associated counterion (e.g., Sepia melanin--K+ form). The method reported here avoided extremes in pH and temperature, and was designed to yield melanin in the K+ form. Physical disaggregation of particulate melanin using a wet milling step was also found to facilitate removal of significant quantities of adsorbed protein. The following physical parameters were used to monitor the purification and to characterize the resultant melanin: pH, conductance, particle size, and diffuse reflectance spectroscopy.