LYCOS RETRIEVER 
Albinism: Melanin
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Albinism results when the body is unable to produce or distribute pigment, called melanin, because of one of several possible genetic defects. In Type 1 albinism, defects in the metabolism of tyrosine lead to failure in converting this amino acid to melanin. This is due to a genetic defect in tyrosinase -- the enzyme responsible for metabolizing tyrosine.
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Albinism consists of a group of inherited abnormalities of melanin synthesis typically characterized by a congenital reduction or absence of melanin pigment. This condition results from defective production of melanin from tyrosine through a complex pathway of metabolic reactions.
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Albinism was formerly categorized as tyrosinase-positive or -negative. In cases of tyrosinase-positive albinism, the enzyme tyrosinase is present. The melanocytes (pigment cells) are unable to produce melanin for any one of a variety of reasons that do not directly involve the tyrosinase enzyme. In tyrosinase-negative cases, either the tyrosinase enzyme is not produced or a nonfunctional version is produced. This classification has been rendered obsolete by recent research.[3]
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Melanin