Albinism Melanocyte

Copper is a component of many enzymes including amine oxidase, lysyl oxidase, ferroxidase, cytochrome oxidase, dopamine P-hydroxylase, superoxide dismutase and tyrosinase. This latter enzyme is present in melanocytes and is important in formation of melanin controlling the colour of skin, hair and eyes. Deficiency of tyrosinase in skin leads to albinism. Cu " ion plays an important role in collagen formation. 

Albinism The most common type, oculocutaneous albinism, results in white hair, pink skin, and an extreme photophobia owing to lack of pigment in the eye Tyrosinase of the melanocyte is absent... 

Albinism is an example of a genetic defect with serious consequences. The enzyme tyrosinase is deficient. Consequently, melanin, a black pigment found in skin, hair, and eyes, is not produced. It is formed from tyrosine in several cell types, for example, the melanocytes in skin. In such cells, tyrosinase converts tyrosine to DOPA and DOPA to dopaquinone. A large number of molecules of the latter product, which is highly reactive, condense to form melanin. Because of the lack of pigment, affected individuals (called albinos) are extremely sensitive to sunlight. In addition... 

Tyrosine also has an important role in the central nervous system and melanocyte and is the precursor of both melanins and catecholamines (epinephrine and norepinephrine). The conversion to these products takes place in the appropriate tissues, usually melanocyte, the central nervous system, or the adrenal gland. In each of these tissues, the enzyme tyrosinase catalyzes the conversion of tyrosine to dihydroxyphenylalanine (DOPA) by hydroxylating the ring adjacent to the parahydroxy group. This is a catechol ring. If this were an amine instead of an amino acid, it would be a catecholamine. The DOPA is a precursor of catecholamines in the adrenal gland and central nervous system. In melanocyte, the DOPA is converted to melanine. In the disease albinism, the tyrosinase in the... 

Catecholamine formation. The conversion of tyrosine to catecholamines and melanins is outlined above. The purple lettering under an enzyme indicates the resulting disease when that enzyme is missing. In the case of albinism, an isoenzyme of tyrosinase is missing in the melanocyte, but not in other tissues. 

A much rarer disease is an inherited defect in the production of lysosomes leading to clinical features due to a resulting malfunction of melanocytes (albinism), platelets (mild bleeding disorders), and phagocytes (lowered resistance to bacterial infection). This is known as Chediak-Higashi disease and is usually fatal in the first or second decade due to uncontrolled infection, but some patients have had their microcidal defect corrected by large doses of ascorbic acid (20 mg per kg body weight per day). 

In albinism, either the copper-dependent tyrosine hydroxylase of melanocytes (which is distinct from the tyrosine hydroxylase found in the adrenal medulla) or other enzymes that convert tyrosine to melanins may be defective. Individuals with albinism suffer from a lack of pigment in the skin, hair, and eyes, and they are sensitive to sunlight. 

Albinism is a condition characterized by total or partial absence of melanin at its normal sites—skin, sclera, etc. Melanin is elaborated by the melanocyte, a special type of cell that originates from the neural crest in the embryo. The cells are found in the skin, in the uveal tract, and in the retina [89, 90]. 

Albinism may involve all melanocytes in the body or may be restricted to a few groups of cells. Clinicians thus describe oculocutaneous and ocular albinism. 

There are two forms of oculocutaneous albinism a tyrosinase negative due to a tyrosinase defect and a tyrosinase positive of unknown origin (probably caused by inavailability of tyrosine to the melanocyte). Both forms are inherited as autosomal recessive traits, but the genes for each type are found in different loci. Ocular albinism is inherited as an X-linked recessive trait. It is associated with vision defects, nystagmus, and head nodding. The metabolic defect is unknown. 

An enzyme involved in the conversion of tyrosine to melanin. One form of albinism is due to a deficiency of tyrosinase in melanocytes. 

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