Determination of 5-S-cysteinyldopa in melanomas with a fluorimetric method.

Differences in color of the skin and hair of animals have been the subject of much research. Such differences have been ascribed partly to differences in the relative amounts of dark eumelanins, and lighter pigments, phaeomelanins, in the pigmented tissues. The chemistry of eumelanins has been extensively discussed in the classic monograph of Nicolaus (1). The early work of Prota and Nicolaus suggested that phaeomelanins were derived from tyrosine and cysteine (2). All later studies lent support to their view. At the VIIth International Pigment Cell Conference in Seattle in 1969, Prota presented the review "Structure and biogenesis of phaeomelanins" (3), which summarizes the very important work in this field from the Department of Organic Chemistry in the University of Naples. In 1966 two catechols giving different fluorophores when oxidized were described in human melanomas (4-6). One of them proved to be dopa, while the other remained unidentified for many years. Recent work has shown that this second catechol is 5-S-cysteinyldopa (7-9), the compound considered to be the building-stone of phaeomelanins. This review concerns studies on 5-S-cysteinyldopa, which suggest that determination of this thiocatechol may be helpful in the definition of pigment metabolism in health and in disease.