| Popis: |
Although the human hair shows a wide range of color hues, microscopic examination has revealed only two types of pigment granules: brown and black (eumelanosome) and yellow and red (phaeomelanosome) (Jimbow et al. 1983). In mice, the genetic pattern of hair color indicates that brown and black pigment granules are controlled by single genetic loci, whereas yellow and red pigment granules are controlled by other genetic loci. Therefore, there may be two separate, but possibly interrelated, metabolic pathways for the two types of pigment granules in man. It is known that brown and black pigments are derived from the enzymatic oxidation of tyrosine to melanin. Although the structure of phaeomelanin may be species specific, and phaeomelanin in the chick may not be the same as that of human hair, animal experiments on this point have yielded valuable information. Prota and Nicolaus (1967) have demonstrated that phaeomelanin of New Hampshire chick feather is a polymer of cystenyldopa which could be formed by the reaction of an amino acid containing thiol group with dopaquinone produced by the enzymatic oxidation of tyrosine. |
