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Int. J. Mol. Sci. 2016, 17(9), 1576; doi:10.3390/ijms17091576

Reactivities of Quinone Methides versus o-Quinones in Catecholamine Metabolism and Eumelanin Biosynthesis

Department of Biology, University of Massachusetts Boston, Boston, MA 02125, USA
Academic Editor: David Arráez-Román
Received: 18 August 2016 / Revised: 8 September 2016 / Accepted: 12 September 2016 / Published: 20 September 2016
(This article belongs to the Special Issue Biochemistry and Mechanisms of Melanogenesis)

Abstract

Melanin is an important biopolymeric pigment produced in a vast majority of organisms. Tyrosine and its hydroxylated product, dopa, form the starting material for melanin biosynthesis. Earlier studies by Raper and Mason resulted in the identification of dopachrome and dihydroxyindoles as important intermediates and paved way for the establishment of well-known Raper–Mason pathway for the biogenesis of brown to black eumelanins. Tyrosinase catalyzes the oxidation of tyrosine as well as dopa to dopaquinone. Dopaquinone thus formed, undergoes intramolecular cyclization to form leucochrome, which is further oxidized to dopachrome. Dopachrome is either converted into 5,6-dihydroxyindole by decarboxylative aromatization or isomerized into 5,6-dihydroxyindole-2-carboxylic acid. Oxidative polymerization of these two dihydroxyindoles eventually produces eumelanin pigments via melanochrome. While the role of quinones in the biosynthetic pathway is very well acknowledged, that of isomeric quinone methides, however, remained marginalized. This review article summarizes the key role of quinone methides during the oxidative transformation of a vast array of catecholamine derivatives and brings out the importance of these transient reactive species during the melanogenic process. In addition, possible reactions of quinone methides at various stages of melanogenesis are discussed. View Full-Text
Keywords: catecholamine metabolism; quinone methides; quinone isomerization; eumelanin biosynthesis; dihydroxyindole polymers; quinone reactivity catecholamine metabolism; quinone methides; quinone isomerization; eumelanin biosynthesis; dihydroxyindole polymers; quinone reactivity
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Sugumaran, M. Reactivities of Quinone Methides versus o-Quinones in Catecholamine Metabolism and Eumelanin Biosynthesis. Int. J. Mol. Sci. 2016, 17, 1576.

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