Insect cuticular melanins are distinctly different from those of mammalian epidermal melanins

Summary

Melanin from several insect samples were isolated and subjected to chemical degradation and HPLC analysis for melanin markers. Quantification of different melanin markers reveals that insect melanins are significantly different from that of the mammalian epidermal melanins. The eumelanin produced in mammals are derived from the oxidative polymerization of both 5,6-dihydroxyindole and 5,6-dihydroxyindole-2-carboxylic acid. The pheomelanin is formed by the oxidative polymerization of cysteinyldopa. Thus dopa is the major precursor for both eumelanin and pheomelanin in mammals. But insect eumelanin appears to be mostly made from 5,6-dihydroxyindole and originate from dopamine. More importantly, our study points out the wide spread occurrence of pheomelanin in many insect species. In addition, cysteinyldopamine and not cysteinyldopa is the major precursor for insect pheomelanin. Thus both eumelanin and pheomelanin in insects differ from higher animals by using dopamine and not dopa as the major precursor.

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