Afroscientific

Melanin: a basic overview

Melanin is a chemical compound that is distributed widely throughout the animal and plant cosmos. The first thing to state about melanin is that, while many of its functions have been described by scientists, its basic structure remains something of mystery even after well over a century of investigation.

 

The number of melanocytes in skin is about the same between ethnic groups. The differences are in the number, size and dispersal of melanosomes.

 

“[T]he structure of melanin remains poorly defined. Classical biophysical methodologies cannot be applied to decipher the structure of melanin because this polymer is insoluble in aqueous or organic fluids and any attempt at solubilization disrupts its structure. Although melanins have ordered local structures their long-range organization is amorphous, and consequently their structures cannot be solved by X-ray crystallography. Melanins are typically dark in color (usually black or brown), acid resistant and bleached by oxidizing agents (Nicholaus et al., 1964Prota, 1992Butler and Day, 1998). The inability to define melanin based on solution-state or crystallographic techniques has prompted the use of alternative approaches to their structural characterization, including electron paramagnetic resonance (EPR) spectroscopy that capitalizes on the presence of a stable organic free radical signature (Enochs et al., 1993).” (Nosanchuk et al., 2015)

What we do know is that melanin ‘polymer’ which means it is a formed of a large number of different molecules (monomers) joined together in a long chain. Melanin-containing tissues have been found in various other parts of the body including the heart, lungs, liver, brain, central nervous system, the larynx and esophagus. “In dark-skinned ethnic groups, melanin also has been found in the lymphatic system draining the skin” (Yerger and Malone, 2006:488).

In the human body, there are at least three main types of melanin which have been labelled eumelanin, pheomelanin and neuromelanin. Eumelanin and pheomelanin are produced in cells called melanocytes which are found in the skin and hair follicles as well as in mucosa, cochlea of the ear, iris of the eye, the mesencephalon of the brain (Yamaguchi and Hearing, 2014:2) the heart and other areas including adipose tissue (e.g. fat) (Brenner & Hearing, 2009:2

Melanocytes produce melanin granules inside organelles called melanosomes. This complex process involving a number of stages is known as melanogenes. Videira et al (2013) describe these various stages in detail and also highlight many of the disorders that arise due to genetic defects in the process.

“There are two distinct types of melanocytes: differentiated melanocytes that originate from the neural crest and can be found at various locations in the body, and a second type, the retinal pigment epithelium (RPE), specifically present only as a single layer of cells lying behind the retina that develop in situ from the optic cup of the brain. The RPE plays a critical role in the active phagocytosis and turnover of the rod outer segments of the retina as well as in the uptake, processing and transport of retinoids and consequently has an important function in vision.” (Brenner & Hearing, 2009:2)

 

 

References

Brenner, M. & Hearing, J. (2009). What are melanocytes really doing all day long…? : from the ViewPoint of a keratinocyte: Melanocytes – cells with a secret identity and incomparable abilities. Experimental Dermatology, Volume 18(9), pp. 799–819. [Full text:  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2792575/ accessed 21/08/18]

Nosanchuk, et al., (2015). Fungal Melanin: What do We Know About Structure? Frontiers in Microbiology, 6:1463. [Full Link: https://www.frontiersin.org/articles/10.3389/fmicb.2015.01463/full accessed 26/08/18]

Videira, I. et al. (2013). Mechanisms regulating melanogenesis. Anais Brasileiros do dermatologia, Volume 88 (1), pp.76-83. [Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3699939/#__ffn_sectitle accessed 22/08/18]

Yamaguchi, Y and Hearing, v. (2014). Melanocytes and their diseases. Cold Spring Harbor Perspectives on Medicine,Volume 4(5), a017046.  [Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3996377/ accessed 21/08/18]

Yerger, V. and Malone, R. (2006). Melanin and Nicotine: a review of the literature. Nicotine & Tobacco Research Volume 8(4), pp.487–498. [Abstract: https://academic.oup.com/ntr/article-abstract/8/4/487/1072272?redirectedFrom=fulltext accessed 22/08/18]

 

This post has first been published on Afroscientific.com

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