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  • Chemical analysis of late stages of pheomelanogenesis: conversion of dihydrobenzothiazine to a benzothiazole structure.

Chemical analysis of late stages of pheomelanogenesis: conversion of dihydrobenzothiazine to a benzothiazole structure.

Pigment cell & melanoma research (2009-06-06)
Kazumasa Wakamatsu, Kazumi Ohtara, Shosuke Ito
ABSTRACT

Pheomelanogenesis is a complex pathway that starts with the oxidation of tyrosine (or DOPA, 3,4-dihydroxyphenylalanine) by tyrosinase in the presence of cysteine, which results in the production of 5-S-cysteinyldopa and its isomers. Beyond that step, relatively little has been clarified except for a possible intermediate produced, dihydro-1,4-benzothiazine-3-carboxylic acid (DHBTCA). We therefore carried out a detailed study on the course of pheomelanogenesis using DOPA and cysteine and the physiological enzyme tyrosinase. To elucidate the later stages of pheomelanogenesis, chemical degradative methods of reductive hydrolysis with hydroiodic acid and alkaline peroxide oxidation were applied. The results show that: (1) DHBTCA accumulates after the disappearance of the cysteinyldopa isomers, (2) DHBTCA is then oxidized by a redox exchange with dopaquinone to form ortho-quinonimine, which leads to the production of pheomelanin with a benzothiazine moiety, and (3) the benzothiazine moiety gradually degrades to form a benzothiazole moiety. This latter process is consistent with the much higher ratio of benzothiazole-derived units in human red hair than in mouse yellow hair. These findings may be relevant to the (photo)toxic effects of pheomelanin.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Hydriodic acid, puriss. p.a., ≥67% (T)
Sigma-Aldrich
Hydriodic acid, contains no stabilizer, ACS reagent, 55%
Sigma-Aldrich
Hydriodic acid, 57 wt. %, distilled, 99.999% trace metals basis
Sigma-Aldrich
Hydriodic acid, contains ≤1.5% hypophosphorous acid as stabilizer, ACS reagent, ≥47.0%
Sigma-Aldrich
Hydriodic acid, contains no stabilizer, distilled, 57 wt. % in H2O, 99.99% trace metals basis
Sigma-Aldrich
Hydriodic acid, 57 wt. % in H2O, distilled, stabilized, 99.95%