Biological pigment
Many biological structures, such as skin, eyes, feathers, fur and hair contain pigments such as melanin in specialized cells called chromatophores.
[4][5] The principal pigments responsible are: Plants, in general, contain six ubiquitous carotenoids: neoxanthin, violaxanthin, antheraxanthin, zeaxanthin, lutein and β-carotene.
[7] Lutein is a yellow pigment found in fruits and vegetables and is the most abundant carotenoid in plants.
[10] As the predominant chlorophylls degrade, the hidden pigments of yellow xanthophylls and orange beta-carotene are revealed.
However, both types of organisms share the possession of photosynthetic pigments, which absorb and release energy that is later used by the cell.
Bacteria produce pigments such as carotenoids, melanin, violacein, prodigiosin, pyocyanin, actinorhodin, and zeaxanthin.
Some animals including fish, amphibians and cephalopods use pigmented chromatophores to provide camouflage that varies to match the background.
However, some biological pigments in animals, such as heme groups that help to carry oxygen in the blood, are colored as a result of happenstance.
Pea aphids (Acyrthosiphon pisum),[12] two-spotted spider mites (Tetranychus urticae),[13][14] and gall midges (family Cecidomyiidae)[15] are the only known animals capable of synthesizing carotenoids.
The colors and characteristic absorption of these carotenoprotein complexes are based upon the chemical binding of the chromogen and the protein subunits.
[citation needed] A common carotenoid in animals is astaxanthin, which gives off a purple-blue and green pigment.
Lastly, the lipoglycoprotein and ovoverdin forms a bright green pigment that is usually present in the outer layers of the carapace and the lobster eggs.
It is produced as the amino acid tyrosine is converted into melanin, which is found in the skin, hair, and eyes.
There are two classes of pigments: black and brown insoluble eumelanins, which are derived from aerobic oxidation of tyrosine in the presence of tyrosinase, and the alkali-soluble phaeomelanins which range from a yellow to red brown color, arising from the deviation of the eumelanin pathway through the intervention of cysteine and/or glutathione.
These melanins are possibly polymers which arise from the repeated coupling of simple bi-polyfunctional monomeric intermediates, or of high molecular weights.
This type is only present in squid and fish, and is used to illuminate their ventral surfaces, which disguise their silhouettes from predators.
Chromatophores are color pigment changing cells that are directly stimulated by central motor neurons.
Schematochromes act like prisms, refracting and dispersing visible light to the surroundings, which will eventually reflect a specific combination of colors.
To change the color pigments, transparency, or opacity, the cells alter in form and size, and stretch or contract their outer covering.
Due to damage from UV-A and UV-B, marine animals have evolved to have compounds that absorb UV light and act as sunscreen.
Carotenoids and photopigments both indirectly act as photo-protective pigments, as they quench oxygen free-radicals.
Coloration in invertebrates varies based on the depth, water temperature, food source, currents, geographic location, light exposure, and sedimentation.
Thus, the marine life that resides on deeper waters is less brilliant than the organisms that live in well-lit areas due to the reduction of pigments.
In many chromodorid nudibranchs, they take in distasteful and toxic chemicals emitted from sponges and store them in their repugnatorial glands (located around the mantle edge).
In the nudibranch Nembrotha Kubaryana, tetrapyrrole pigment 13 has been found to be a potent antimicrobial agent.
Sesquiterpenoids are recognized for their blue and purple colors, but it has also been reported to exhibit various bioactivities such as antibacterial, immunoregulating, antimicrobial, and cytotoxic, as well as the inhibitory activity against cell division in the fertilized sea urchin and ascidian eggs.
In fact, two new carotenoids that were isolated from a sponge called Phakellia stelliderma showed mild cytotoxicity against mouse leukemia cells.
Other pigments with medical involvements include scytonemin, topsentins, and debromohymenialdisine have several lead compounds in the field of inflammation, rheumatoid arthritis and osteoarthritis respectively.
