Abstract
Animals synthesize melanin pigments for the coloration of their skin and use it for their protection from harmful solar radiation. Insects use melanins even more ingeniously than mammals and employ them for exoskeletal pigmentation, cuticular hardening, wound healing and innate immune responses. In this review, we discuss the biochemistry of melanogenesis process occurring in higher animals and insects. A special attention is given to number of aspects that are not previously brought to light: (1) the molecular mechanism of dopachrome conversion that leads to the production of two different dihydroxyindoles; (2) the role of catecholamine derivatives other than dopa in melanin production in animals; (3) the critical parts played by various biosynthetic enzymes associated with insect melanogenesis; and (4) the presence of a number of important gaps in both melanogenic and sclerotinogenic pathways. Additionally, importance of the melanogenic process in insect physiology especially in the sclerotization of their exoskeleton, wound healing reactions and innate immune responses is highlighted. The comparative biochemistry of melanization with sclerotization is also discussed.
Highlights
Melanins are a group of widely distributed phenolic biopolymers arising from the amino acid, tyrosine and related phenolic compounds [1,2,3]
The brown to black eumelanins are formed by the oxidative polymerization of dihydroxyindoles that are derived from dopa and its derivatives
A simplistic view of melanogenesis was delineated in the early part of last century by the pioneering work of Raper and Mason
Summary
Melanins are a group of widely distributed phenolic biopolymers arising from the amino acid, tyrosine and related phenolic compounds [1,2,3]. They are responsible for the skin, hair (or coat or feather), and eye color in animals. Animals synthesize three different kinds of melanin viz., pheomelanin, eumelanin and neuromelanin by the action of ubiquitously present enzyme tyrosinase as well as phenoloxidases. Pheomelanin is produced by the oxidative polymerization of cysteinyldopa, which in turn is synthesized by the coupling of enzymatically generated dopaquinone with the amino acid, cysteine. The focus of this article will be limited to the biosynthesis, some functions and comparative biochemistry of melanogenesis and related processes in insects and higher animals
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