Melanin
Melanins are macromolecules that are synthesised during phenolic and/or
indolic chemicals being oxidatively polymerized. These hydrophobic
pigments are negatively charged, which are found throughout the
biological system in a wide range and take part in processes like
structure, colouring, free radical scavenging, radiation resistance, and
thermoregulation. Many bacteria obtained from nature, includingBacillus, Aeromonas , Rhizobium and Streptomyces ,
have been shown to synthesis of melanin using the copper-containing
enzyme tyrosinase (monophenol monooxygenase EC 1.14.18.1) (Wang et al.,
2020). Bacterial melanin is produced by the usage of the enzyme
tyrosinase, which oxidises into L-tyrosine and then converts to L-3,
4-dihydroxyphenylalanine. Finally, the transformed melanin synthesis
takes place through the oxidoreduction process with a colour range of
black to brown (Velmurugan et al., 2020). Melanin is the most stable,
soluble, biochemically resistant, negatively charged, hydrophobic, high
molecular weight, amorphous substance, but it is insoluble in common
organic solvents, aqueous acid and water. There are three types of
melanin based on colour and structural classes: (i) eumelanins (ii)
pheomelanins (iii) allomelanins are colour pigments that range from
black to brown in colour and that are synthesised via the standard.
Pheomelanins are brown, red or yellow coloured pigments which are
produced in the course of oxidation of tyrosine and/or phenylalanine to
dihydroxyphenylalanine (DOPA) and dopaquinone. Pheomelanin results from
cysteinylation of DOPA and these are sulphur-containing compounds.
Allomelanins include nitrogen-free heterogeneous groups of polymers
formed from catechol precursors. They are found in microorganisms and
plants, whereas eumelanins and pheomelanins are found in animals only
(Tarangini & Mishra, 2013). Microorganisms used melanin to protect
themselves from heat, chemical (heavy metals and oxidising agents),
enzymatic lysis, alveolar macrophages. There is a wide range of
applications by using melanin in the fields of antimicrobial, antiviral,
anticancer, antioxidant and anti-inflammation assays. Melanin has a high
absorbing capacity of electromagnetic radiation, viz., visible light,
ultraviolet radiation, and X-rays because of this property, the
pharmaceutical and cosmetic industries use it in huge amounts. It has
the ability to bind heavy metals and radionuclides (Wang et al., 2020),
Which is used in the recycling of heavy metal-contaminated waste water.
The mass production of melanin pigment is in high demand due to its
significant bioactive potential properties and capacity to be employed
in a wide range of applications. Furthermore, marine biological
organisms as a major source for the synthesis of melanin pigment is an
intriguing choice for both researchers and industries for its increased
number of characteristics, including being safe, easily degradable and
eco-friendly without causing severe side effects (Elsayis et al., 2022).