General Characteristics of Melanin Pigments of Fungal Origin

CHAPTER 1 LITERATURE REVIEW

1.1 General Characteristics of Melanin Pigments of Fungal Origin

A class of sophisticated, heterogeneous polymers extensively found in nature are melanin pigments. Organisms from all biological kingdoms, including fungus, synthesis them. Although their pigmentation properties define these biopolymers most, their roles also include important physiological and protective ones. Melanins are involved in a wide spectrum of activities in fungus, from pathogenicity to survival under very hostile environments.

1.1.1 Definition and Structure of Fungal Melanins

Comprising complex biopolymers with great degrees of structural and functional variability, fungal melanins are Classed as secondary metabolites, they play specialized roles improving survival in particular environments rather than being necessary for the development or reproduction of fungus. Extensive π-electron conjugation within their polymeric structure produces their characteristic dark pigment, which spans brown to black. Along with their color, this conjugation supports many of their unusual chemical and biological characteristics, including stability under highly demanding environmental conditions and the capacity to absorb a wide spectrum of light, especially ultraviolet radiation.

Structurally, fungal melanins are amorphous heteropolymers devoid of a clearly defined chemical formula since their polymerization patterns differ greatly among species. Usually derived from the oxidative polymerization of phenolic or indolic monomers—which create irregular linkages between repeating units—these polymers Variations in the precursor molecules used during biosynthesis as well as the enzymatic and environmental elements affecting the polymerization process define the heterogeneity in their structure. Melanins' adaptability in biological systems is attributed in part to their ability to incorporate different chemical functionalities including hydroxyl, carboxyl, and quinone groups. Further adding to their functional variety and stability are fungal melanins, which frequently chelate metal ions including iron, copper, and manganese [1].

Fungal melanins show a larger spectrum of precursor molecules and polymerizing patterns than those of plant and animal melanins. Based on their biosynthesis, these variations produce three main categories for fungal melanins: eumelanins, pheomelanins, and allomelanins. Made from