Biological Pigments, Biochromes

Biological pigments are colored substances which are either produced inside the living cells or introduced from the environment. Most biological pigments are grouped into no more than six kinds of structures: tetrapyrroles, isoprenoids, quinones, benzopyrans, N-heterocyclic compounds, and metalloproteins. Scientific reports have described 34 tetrapyrroles, over 600 carotenoids, more than 4,100 flavonoids, and within this group over 250 anthocyanins. Quinones are also widely distributed. Chlorophylls and carotenoids are the most abundant pigments in nature. They are involved in fudamental processes, and life on Earth depends on them. Three basic classes of biochromes are able to capture energy to carry out photosynthesis: chlorophylls, carotenoids, and phycobilins. he following list of biological pigments represents biological pigments commonly found in plant and animal cells.

  • Adrenochrome - melanine-like pigment; metabolite of epinephrine; hallucinogen; highly reactive neurotoxin; antagonist of the hormone triiodothyronine and can damage the thyroid; generates free radicals.
  • Anthocyanins - a group of about 250 water-soluble biochromes of the flavonoid family present in plant cell fluids; responsible for bright colors (red, orange, blue); widely distributed in fruits, especially in berries.
  • Bile Pigments - bilirubin and biliverdin, products of degradation of heme that was present in hemoglobin; metabolically derived from porphyrins.
    • Bilirubin
    • Urobilin - a brownish pigment formed by oxidation of urobilinogen, a product of metabolism of bilirubin formed in the intestines.
  • Carotenoids - second most abundant class of biochromes present in photosynthetic and non-photosynthetic tissues; frequently contained within special pigment cells called xanthophores. They are yellow, orange or red, found in most photosynthesizing cells.
    • beta Carotene - yellow or orange; precursor of vitamin A; antioxidant.
    • Lycopene - red; a carotenoid with a strong antioxidant activity.
    • Retinoids - originate from carotenoids; obtained exclusively from the diet as vitamins and are best known as visual pigments involved in signal transduction in the retina; some participate in regulation of gene expression (retinoic acid).
      • Acitretin - synthetic second-generation retinoid, metabolite of etretinate, used in the treatment of severe psoriasis.
      • Fenretinide - synthetic retinoid, structurally related to vitamin A, with biological effects in the controlling of cell proliferation.
      • Isotretinoin - synthetic retinoid used in the treatment of cystic acne.
      • Retinaldehyde - precursor of retinoic acid; product of metabolism of beta-carotenes.

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      • Tretinoin - naturally occurring form of vitamin A; used in the treatment of promyelocytic leukemia.
      • Vitamin A
    • Xanthophylls - accessory yellow pigments of plants; oxygenated derivatives of carotenes; animals obtain them from food.
      • Canthaxanthin - Β-carotene-4,4'-dione; feed additive used in farmed salmon and shrimp.
      • Lutein - macular pigment of the human retina; present in all plants.
      • Zeaxanthin - macular pigment of the human retina.
    • zeta Carotene - precursor of beta carotene.
  • Ceroid - yellow decomposition pigment found in cells.
  • Flavins - ubiquitous class of coenzymes; important in (de)hydrogenation and hydroxylation reactions, detoxification, regulation of biological clocks, and programmed cell death 6.
  • Hemocyanin - blue pigment containing copper ions; found in the plasma of molluscs.
  • Lipofuscin - age pigment, wear and tear pigment; products of oxidation of lipids in lysosomes which consist of proteins and partly oxidized polyunsaturated fatty acids that form intracellular clusters of yellowish granules; deposited continuously throughout life in nerve, heart and liver cells, as well as other organs.
  • Melanins - black or brown polymers, most widespread pigments in animals.
  • Phycocyanin - water-soluble blue pigment-protein complex (chromoprotein) with the absorption maximum in between 615 and 635 nm. Cyanobacteria phycocyanin (C-phycocyanin) is found mainly in cyanobacteria and R-phycocyanin is found mainly in red algae (Rhodophyta). C-phycocyanin is thought to have antioxidant activity.
  • Phycoerythrin - orange pigment-protein complex (chromoprotein); three types of phycoerythrin include: C, B, and R. R-phycoerythrin is found mostly red algae (Rhodophyta); B-phycoerythrin is found in Bangiales, a family of algae in Rhodophyta class; C-phycoerythrin is found in Cyanophyta class.
  • Phytochromes - red/far-red light-absorbing, intensely colored pigments in plants located in seed embryos; enable seeds to sense even the dim light deep beneath the surface of the soil and allow leaves to perceive moonlight. In light-grown plants, phytochromes allow for the perception of light intensity. Phytochromes B through D are light-stable 7.
    • Cryptochrome - blue light-absorbing pigment in plants.
    • Phytochrome A - photoactive protein which has many biological functions; unstable in light; produced initially in the dark in the red-light absorbing form (Pr). Upon exposure to red light (600 nm), Pr is converted to Pfr, the biologically active form, which absorbs far red light (720 nm) 8.
    • Phytochrome B - absorbs light at specific wavelengths (660 and 730 nm); inhibits phytochrome A.
    • Phytochrome C - plays a role in tropisms in seedlings and inflorescence stems of light-grown plants; has a positive effect on gravitropism in hypocotyls and stems, but has a limited role in root gravitropism 9.
    • Phytochrome D - controls elongation growth and flowering time; inhibits phytochrome A.
    • Phytochrome E - controls light-induced germination; does not inhibit phytochrome A.
  • Porphyrins - water-soluble, nitrogenous compounds which are considered as porphin derivatives where hydrogens are substituted by side chains. Porphyrins are classified on the basis of these side chains. Many metal ions are complexed with porphyrins, forming metalloporphyrins. Chlorophylls and bacteriochlorophylls are magnesium complexes of various porphyrins.
    • Chlorophylls - group of five, closely related green pigments, designated a through e, which are the most abundant biological pigments in nature. They function as photoreceptors of light energy in photosynthesis. The principal chlorophyll is chlorophyll a.
      • Bacteriochlorophylls - four pigments (a-d) found in photosynthetic bacteria which are different from chlorophyll-a present in plants and algae. Bacteriochlorophylls -a and -b are mostly found in purple sulfur and non-sulfur bacteria; bacteriochlorophylls -c and -d are typically found in green sulfur bacteria 19.
      • Chlorophyllides - green pigments, products of the hydrolysis of chlorophylls by means of naturally occurring enzyme chlorophyllase.
      • Hemerythrin - red pigment containing iron ions; found in blood cells of annelids.
      • Protochlorophyllide - photo-active pigment localized in prolamellar bodies occurring within the proplastids of dark-grown bean leaves. In the process of photoconversion, the highly fluorescent protochlorophyllide is converted to chlorophyll 11.
    • Coproporphyrins - decomposition products of bilirubin, found normally in feces. The type I isomer, a side product, is excreted in the feces and urine in congenital erythropoietic porphyria; the type III isomer, an intermediate in heme biosynthesis, is excreted in the feces and urine in hereditary coproporphyria and variegate porphyria.
    • Deuteroporphyrins - protoporphyrins; deuteroporphyrin III is the protoporphyrin of heme, the only known naturally occurring isomer of etioporphyrin III.
    • Etioporphyrins - synthetic porphyrins.
    • Hematoporphyrins - iron-free derivatives of heme; some of these photosensitizing agents are used in the phototherapy of cancers. Hematoporphyrin IX was the first porphyrin isolated (1867) by treatment of blood with concentrated sulfuric acid.
    • Mesoporphyrins - porphyrins with four methyl, two ethyl, and two propionic acid side chains attached to the pyrrole rings.
    • Metalloporphyrins - porphyrins with metals and metalloids inserted into the central hole of the porphyrin macrocycle. They are very stable and can bind small molecules (ligands) to the central metal atom. They are studied as blood substitutes and electrocatalysts for fuel cells 7.
      • Chlorophylls
      • Heme - insoluble iron protoporphyrin constituent of hemoglobin, other respiratory pigments and of many animal and plant cells.
    • Protoporphyrins - porphyrins whose iron complexes united with proteins occur in hemoglobin, myoglobin, and certain respiratory pigments.
    • Uroporphyrins - produced during the synthesis of natural porphyrins; excreted in urine.
  • Prodigiosin - a naturally occurring red, hydrophobic, anion-carrier molecule; facilitates the transmembrane transport of Clorine (Cl-) and bicarbonate (HCO3-) ions; present in certain bacteria (Serratia marcescens, Vibrio spp.); has antimicrobial and algicidal activities.
  • Pterins - pteridines with the structure 2-amino-4-oxo; include redox cofactors biopterin, molybdopterin, and various insect pigments. There are two groups of pterins: conjugated and unconjugated. The most important blue-fluorescing pterins are neopterin, monapterin, biopterin, isoxanthopterin, primapterin and pterin. Measurement of pterins in different biological fluids is the most common method for screening and diagnosis of inborn errors of BH4 (tetrahydrobiopterin) metabolism 15.
    • Xanthopterin - yellow-fluorescing pterin.
    • Neopterin - secreted by macrophages; elevated excretion of neopterin is associated with certain cancers, viral infection and graft rejection.
  • Pyocyanine - antibiotic pigment produced by Pseudomonas aeruginosa.
  • Retinal Pigments - pigments found in retinal photoreceptors (rods and cones) that are either of photoreceptor or non-photoreceptor type.
    • Photoreceptor retinal pigments - rhodopsinlike pigments plus a variable number of cone pigments in most animals. Mammals typically have only two, a short-wavelength pigment absorbing in the ultraviolet, violet, or blue region, and a long-wavelength pigment with maximum absorption in the green and red region 18.
      • Rhodopsins - light-sensitive pigments; consist of opsin proteins, which behave as enzymes, and a small carotenoid molecule retinal, a derivative of vitamin A.
    • Non-photoreceptor retinal pigments - include pinopsin, parapinopsin, peropsin, melanopsin, neuropsin, encephalopsin vertebrate ancient opsin, and teleost multiple tissue opsin; their functions are poorly understood.


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