Mutagenicity of melanin from human red hair.

The Salmonella typhimurium histidine reversion test of Ames et al. was used to demonstrate the pheomelanin, the red-brown polymeric pigment produced in human skin and hair, becomes mutagenic after exposure to long wave-length UV-light; a finding consistent with the UV-induced somatic mutation hypothesis for the origin of freckles and the high susceptibility of redheads and blonds to sunlight-induced skin cancers.

Photodestruction of pheomelanin: role of oxygen.

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 phemelanin 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.

Genetic and environmental determinants of skin color.

Skin reflectance measurements on a sample of 154 Black and 191 White same-sex twin pairs, attending Philadelphia area schools, are analyzed to determine the effects of genetic and environmental factors. The measurements obtained in July and August, on the forehead, inner upper arm, and flexor surface of the forearm with red, green, and blue filters, were reduced to one index which we call skin color. Analysis of this index using the path analysis of Rao et al. ('74) estimates the major variance components due to racial, residual genetic, and common environmental factors as 67%, 5%, and 22%, respectively.

Skin reflectance in the newborn infant.

Skin reflectance in red, green, and blue light was measured at the sternum of 99 Caucasian infants ranging in gestational age from 26 to 44 weeks. Skin reflectance was consistently higher in female infants, but this difference was not statistically significant. Highly significant (P less than 0.001) increases in reflectance at all wave lengths were found when sternal reflectance during the first 48 hr of life was related to gestational age. The dispersion of data points about the regression line does not permit this method to be relied upon as the sole means of determining gestational age of infants. Serial studies indicate that reflectance increases in premature infants not given phototherapy, whereas premature infants receiving phototherapy show a fall in reflectance for the duration of therapy. This suggests that phototherapy may cause tanning of the skin.

A quantitative and morphological study of the pigmentary system of the chimpanzee with the light and electron microscope.

The epidermal melanocyte system of the chimpaneze was studied by the combined skin-splitting DOPA, and electron microscopic techniques. It is very similar to man. There are DOPA-positive epidermal melanocytes in all body regions regradless of the degree of macroscopic skin pigmentation or hirsutism. Furthermore, as in man, but in contrast to rodents, chimpanzee skin contains a very high level of melanocytes in the epidermis; approximately 3,320+/-350 per square millimeter skin. Chimpanzee melanosomes are long, wide, and fully melanized. In keratinocytes, these organelles are individually dispersed in all body regions, regardless of the degree of skin color, as is true for other mammalian species with large melanosomes.