Sköld HN, Aspengren S, Cheney KL, Wallin M (2016). "Chapter Four - Fish Chromatophores—From Molecular Motors to Animal Behavior". International Review of Cell and Molecular Biology. 321: 171–219. doi: 10.1016/bs.ircmb.2015.09.005. Hegna, Robert H.; Nokelainen, Ossi; Hegna, Jonathan R.; Mappes, Johanna (2013). "To quiver or to shiver: increased melanization benefits thermoregulation, but reduces warning signal efficacy in the wood tiger moth". Proc. R. Soc. B. 280 (1755): 20122812. doi: 10.1098/rspb.2012.2812. PMC 3574392. PMID 23363631. Because melanin is an aggregate of smaller component molecules, there are many different types of melanin with different proportions and bonding patterns of these component molecules. Both pheomelanin and eumelanin are found in human skin and hair, but eumelanin is the most abundant melanin in humans, as well as the form most likely to be deficient in albinism. [7] Eumelanin [ edit ] Part of the structural formula of eumelanin. "(COOH)" can be COOH or H, or (more rarely) other substituents. The arrow denotes where the polymer continues. Yao, Zeng-Yu; Qi, Jian-Hua (22 April 2016). "Comparison of Antioxidant Activities of Melanin Fractions from Chestnut Shell". Molecules. 21 (4): 487. doi: 10.3390/molecules21040487. PMC 6273334. PMID 27110763. Mouchet, Sébastien R; Deparis, Olivier (2021), Natural Photonics and Bioinspiration (1sted.), Artech House, ISBN 978-163-081-797-8

Mylonakis, E. et al. Galleria mellonella as a model system to study Cryptococcus neoformans pathogenesis. Infect. Immun. 73, 3842–3850 (2005). Following the hemocyte washes, 1 ml of cell-free hemolymph was added to the entirety of the MatTek dish, followed by an addition 1 ml of IPS. The MatTek dish was covered and imaged using the OpenFlexure microscope and software and time-lapse microscopy was performed every minute for 16–24 h 63. Control experiments without added fungus or fungal components, or with anticoagulation buffer to inhibit melanization and coagulation, were performed (Supplementary Movies 11 and 12). This protocol is summarized in Supplementary Fig. 3b. Barillas-Mury, C. CLIP proteases and Plasmodium melanization in Anopheles gambiae. Trends Parasitol. 23, 297–299 (2007). Kim, Y.-J.; Uyama, H. (15 May 2005). "Tyrosinase inhibitors from natural and synthetic sources: structure, inhibition mechanism and perspective for the future". Cellular and Molecular Life Sciences. 62 (15): 1707–1723. doi: 10.1007/s00018-005-5054-y. PMID 15968468. S2CID 8280251.

Prodigiosin

In addition to melanin deficiency, the molecular weight of the melanin polymer may be decreased by various factors such as oxidative stress, exposure to light, perturbation in its association with melanosomal matrix proteins, changes in pH, or in local concentrations of metal ions. A decreased molecular weight or a decrease in the degree of polymerization of ocular melanin has been proposed to turn the normally anti-oxidant polymer into a pro-oxidant. In its pro-oxidant state, melanin has been suggested to be involved in the causation and progression of macular degeneration and melanoma. [58] Rasagiline, an important monotherapy drug in Parkinson's disease, has melanin binding properties, and melanoma tumor reducing properties. [59] Within nodules of encapsulated GFP-positive C. neoformans extracted from the hemolymph of infected G. mellonella, we measured the degree of immune melanin intensity and GFP fluorescence intensity. We found that the yeast with weaker GFP signal were associated with greater melanin encapsulation, in contrast to the population of brightly fluorescent cells that were not encapsulated with as much, or any, melanin (Fig. 1e), thus identifying an inverse correlation between degree of melanin encapsulation and fluorescence within GFP-positive cells. The occurrence of faint signal in some cells may suggest that cells are undergoing cell death or have recently been killed.

Donatien PD, Orlow SJ (August 1995). "Interaction of melanosomal proteins with melanin". European Journal of Biochemistry. 232 (1): 159–64. doi: 10.1111/j.1432-1033.1995.tb20794.x. PMID 7556145. We observed that some of the melanin-encapsulated C. albicans yeast survived the immune reaction and then underwent hyphal and/or pseudohyphal growth (Fig. 5d, Supplementary Movie 9). This occurred in about 23% of melanin-encapsulated yeast, with 8% of single yeast and 38% of budded/pairs of yeast being able to escape (Fig. 5e) The time until hyphal or pseudohyphal growth was significantly delayed in the melanin-encapsulated cells; the average time for a non-melanin-encapsulated C. albicans cells to begin filamentation is 92 min, while the melanin-encapsulated counterparts take 265 min, with some taking as long as 520 min (Fig. 5f). This delay could be reflective of physical barriers as the fungus breaks through the melanin layer and/or delays in initiating cellular growth because of cell damage caused by the immune response. Zhang, J. et al. Prophenoloxidase-mediated ex vivo immunity to delay fungal infection after insect ecdysis. Front. Immunol 8, 1445 (2017). Meneely, Philip (2014). Genetic Analysis: Genes, Genomes, and Networks in Eukaryotes. Oxford University Press. ISBN 9780199681266.During cryptococcal infection of G. mellonella, melanin encapsulation of the fungus within nodules was associated with diminished or lost fluorescence signal in these GFP-expressing C. neoformans strains. Additionally, the melanin-encapsulated fungi that remained GFP-positive had weaker signals and the intensity of the GFP signal was more intense for the non-melanin-encapsulated fungi within the nodules. The expression of GFP in these cells is under the control of an actin promotor, and while actin is generally presumed to be constitutively expressed in cells, growth conditions have been shown to lead to some alterations in cryptococcal actin expression 49, 50. If the environmental conditions within the nodule abolished actin expression in some cells without killing the fungus, we would expect that condition to equally affect the melanin and non-melanin-encapsulated fungi, and as a result, see similar GFP-negative: GFP-positive ratios between the melanin-encapsulated and not melanin-encapsulated cells. The association between melanin encapsulation and disappearance in GFP fluorescence provides strong evidence for the notion that the melanization reaction kills fungal cells during infection. This is the first evidence, to the best of our understanding, that G. mellonella immune melanization directly and effectively neutralizes C. neoformans during infection and demonstrated that melanin encapsulation results in fungal death within the insect. Previously, the death of microbes, specifically bacteria, was attributed to the enzymatic activity of the melanin-producing phenoloxidase (PO) in an in vitro reaction 16. In addition to our association of melanin encapsulation and fungal death in vivo, we sought to reproduce these results in vitro using extracted hemolymph in buffer. We used the PO-specific inhibitor, phenylthiourea (PTU), we found that PO-inhibited wells of hemolymph had higher recoverable CFUs of C. neoformans compared to the uninhibited wells. The inverse correlation of melanization with CFUs further supports the claim that melanin plays a role in neutralizing C. neoformans. Since we only assayed CFUs from these in vitro experiments, we cannot determine whether the melanization in the in vitro experiments directly killed the fungus or just inhibited fungal growth. Neuromelanin. While eumelanin and pheomelanin control the colors of things you see (such as skin, hair and eyes), neuromelanin is responsible for the color of your neurons. Melanin produced by plants are sometimes referred to as 'catechol melanins' as they can yield catechol on alkali fusion. It is commonly seen in the enzymatic browning of fruits such as bananas. Chestnut shell melanin can be used as an antioxidant and coloring agent. [45] Biosynthesis involves the oxidation of indole-5,6-quinone by the tyrosinase type polyphenol oxidase from tyrosine and catecholamines leading to the formation of catechol melanin. Despite this many plants contain compounds which inhibit the production of melanins. [46] Interpretation as a single monomer [ edit ]