Melanins occurrence

From a chemical point of view, and in a very simplified way, in the animal kingdom the so-called eumelanins (or melanins tout-court), black or dark brown, and completely insoluble in water, differ from pheomelanins, that contain sulfur, varying from yellow to brown-red, and alkali-soluble. Both the kinds of melanin can be present at the same time within the same organism. For a deeper insight in melanin occurrence and properties, see [238],... 

Tyrosine (Tyr or Y) (4-hydroxyphenylalanine ((5)-2-amino-3-(4-hydroxyphenyl)-propanoic acid)) is a polar, neutral, aromatic amino acid with the formula H00CCH(NH2)CH2C6H50H and is the precursor of thyroxin, dopamine, norepinephrine (noradrenaline), epinephrine (adrenaline), and the pigment melanin. Being the precursor amino acid for the thyroid gland hormone thyroxin, a defect in this may result in hypothyroidism. Tyr is extremely soluble in water, a property that has proven useful in isolating this amino acid from protein hydrolysates. The occurrence of tyrosine- 0-sulfate as a constituent of human urine and fibrinogen has been reported. ... 

Selective distribution within the body occurs because of special affinity between particular drugs and particular body constituents. Many drugs bind to proteins in the plasma phenothiazines and chloro-quine bind to melanin-containing tissues, including the retina, which may explain the occurrence of retinopathy. Drugs may also concentrate selectively in a particular tissue because of specialised transport mechanisms, e.g. iodine in the thyroid. 

The disease does not result from the absence of melanocytes. In fact, the following evidence suggests that these cells are present (1) demonstration of melanocytes in skin of albinos by histochemical methods (gold impregnation techniques) (2) electron microscopic recognition of melanocytes in albinos skin and (3) the occurrence of amelanotic nevi, or benign tumors. The inability of the albino s melanocyte to produce melanin is not understood. 

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