TYR and melanoma: For example, melatonin may be metabolized through indole and kynurenic pathways to N1-acetyl-N2-formyl-5-methoxykinuramine, 6-hydroxymelatonin and 5-methoxytryptamine in melanoma cells [40], and that the latter metabolite stimulates tyrosinase activity and intracellular melanin content in human SK-MEL-188 [38].