Fundamental aspects of morphological melanin color changes in vertebrate skin.

Abstract

SYNOPSIS. Consideration of some biochemical mechanisms in synthesis of melanin from the biological viewpoint has yielded some insight into various aspects of the problem. A fundamental consideration is the procedure which must unequivocally demonstrate tyrosinase and determine its level of activity with sensitivity and precision. Only the radiometric assay utilizing 14C—abelled L—tyrosine fulfills these criteria. Although integumental tyrosinase activity is usually correlated with the degree of melanoderma, exceptional cases are sufficiently documented to provide a basis for the presence of normal melanogenic control mechanisms in the skin. In addition, the enzyme may not always be bound to a subcellular organelle, thus suggesting its origin is at a distance from its site of action (premelanosome). A number of biological factors affect the enzymatic activity and its subcellular distribution indicating that the biological state of the organism cannot be disregarded in biochemical studies. Further, the use of variously labelled substrates has revealed the poikilopolymeric nature of melanin and the possibility of the direct effect of the intracellular environment upon the nature of the polymer. Several types of primary control mechanisms directly affecting the activity of tyrosinase are present in the vertebrate integument. It is probable that additional mechanisms will be uncovered eventually.