Bilin (biochemistry)
Encyclopedia
Bilins, bilanes or bile pigments are biological pigments formed in many organisms as a metabolic product of certain porphyrin
s. Bilin (also called bilichrome) was named as a bile
pigment of mammal
s, but can also be found in lower vertebrate
s, invertebrate
s, as well as red algae
, green plant
s and cyanobacteria. Bilins can range in color from red, orange, yellow or brown to blue or green.
In chemical terms, bilins are linear arrangements of four pyrrole
rings (tetrapyrrole
s). In human metabolism, bilirubin
is a breakdown product of heme
. Hydroxymethyl bilane is a major anabolic product, from the biosynthetic reaction of porphobilinogen
(PBG) and uroporphyrinogen I synthase (known as porphobilinogen deaminase
).
Examples of bilins are found in animals, and phycocyanobilin
, the chromophore of the photosynthetic pigment
phycocyanin
in algae and plants. In plants, bilins also serve as the photopigment
s of the photoreceptor protein
phytochrome
. An example of an invertebrate bilin is micromatabilin, which is responsible for the green color of the Green Huntsman Spider, Micrommata virescens
.
Porphyrin
Porphyrins are a group of organic compounds, many naturally occurring. One of the best-known porphyrins is heme, the pigment in red blood cells; heme is a cofactor of the protein hemoglobin. Porphyrins are heterocyclic macrocycles composed of four modified pyrrole subunits interconnected at...
s. Bilin (also called bilichrome) was named as a bile
Bile
Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...
pigment of mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, but can also be found in lower vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s, invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, as well as red algae
Red algae
The red algae are one of the oldest groups of eukaryotic algae, and also one of the largest, with about 5,000–6,000 species of mostly multicellular, marine algae, including many notable seaweeds...
, green plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s and cyanobacteria. Bilins can range in color from red, orange, yellow or brown to blue or green.
In chemical terms, bilins are linear arrangements of four pyrrole
Pyrrole
Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H4NH. It is a colourless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., N-methylpyrrole, C4H4NCH3...
rings (tetrapyrrole
Tetrapyrrole
Tetrapyrroles are compounds containing four pyrrole rings. With the exception of corrin, the four pyrrole rings are interconnected through one-carbon bridges, in either a linear or a cyclic fashion...
s). In human metabolism, bilirubin
Bilirubin
Bilirubin is the yellow breakdown product of normal heme catabolism. Heme is found in hemoglobin, a principal component of red blood cells. Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases...
is a breakdown product of heme
Heme
A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are...
. Hydroxymethyl bilane is a major anabolic product, from the biosynthetic reaction of porphobilinogen
Porphobilinogen
Porphobilinogen is a pyrrole involved in porphyrin metabolism.It is generated by aminolevulinate and the enzyme ALA dehydratase. PBG is then converted into hydroxymethyl bilane by the enzyme porphobilinogen deaminase, also known as hydroxymethylbilane synthase.Acute intermittent porphyria causes...
(PBG) and uroporphyrinogen I synthase (known as porphobilinogen deaminase
Porphobilinogen deaminase
Porphobilinogen deaminase is an enzyme involved in the third step of the metabolism of porphyrin, converting porphobilinogen into hydroxymethylbilane. The enzyme has the unique cofactor dipyrromethane...
).
Examples of bilins are found in animals, and phycocyanobilin
Phycocyanobilin
Phycocyanobilin is a blue phycobilin, i.e., a tetrapyrrole chromophore found in cyanobacteria and in the chloroplasts of red algae, glaucophytes, and some cryptomonads. Phycocyanobilin is present only in the phycobiliproteins allophycocyanin and phycocyanin, of which it is the terminal acceptor of...
, the chromophore of the photosynthetic pigment
Photosynthetic pigment
A photosynthetic pigment is a pigment that is present in chloroplasts or photosynthetic bacteria and captures the light energy necessary for photosynthesis.- Plants :...
phycocyanin
Phycocyanin
Phycocyanin is a pigment from the light-harvesting phycobiliprotein family, along with allophycocyanin and phycoerythrin. It is an accessory pigment to chlorophyll. All phycobiliproteins are water-soluble and therefore cannot exist within the membrane as do carotenoids, but aggregate forming...
in algae and plants. In plants, bilins also serve as the photopigment
Photopigment
Photopigments are unstable pigments that undergo a chemical change when they absorb light. The term is generally applied to the non-protein chromophore moiety of photosensitive chromoproteins, such as the pigments involved in photosynthesis and photoreception...
s of the photoreceptor protein
Photoreceptor protein
Photoreceptors are light-sensitive proteins involved in the sensing and response to light in a variety of organisms. Some examples are rhodopsin in the photoreceptor cells of the vertebrate retina, phytochrome in plants, and bacteriorhodopsin and bacteriophytochromes in some bacteria...
phytochrome
Phytochrome
Phytochrome is a photoreceptor, a pigment that plants use to detect light. It is sensitive to light in the red and far-red region of the visible spectrum. Many flowering plants use it to regulate the time of flowering based on the length of day and night and to set circadian rhythms...
. An example of an invertebrate bilin is micromatabilin, which is responsible for the green color of the Green Huntsman Spider, Micrommata virescens
Micrommata virescens
The green huntsman spider is a spider of the family Sparassidae. It does not build a web, and hunts insects in green vegetation, where it is well camouflaged....
.
See also
- BilirubinBilirubinBilirubin is the yellow breakdown product of normal heme catabolism. Heme is found in hemoglobin, a principal component of red blood cells. Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases...
- BiliverdinBiliverdinBiliverdin is a green tetrapyrrolic bile pigment, and is a product of heme catabolism. It is the pigment responsible for a greenish color sometimes seen in bruises.- Metabolism :...
- PhycobilinPhycobilinPhycobilins are chromophores found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads...
- PhycobiliproteinPhycobiliproteinPhycobiliproteins are water-soluble proteins present in cyanobacteria and certain algae that capture light energy, which is then passed on to chlorophylls during photosynthesis. Phycobiliproteins are formed of a complex between proteins and covalently bound phycobilins that act as chromophores...
- PhycoerythrobilinPhycoerythrobilinPhycoerythrobilin is a red phycobilin, i.e. an open tetrapyrrole chromophore found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads. Phycoerythrobilin is present in the phycobiliprotein phycoerythrin, of which it is the terminal acceptor of energy. The...
- StercobilinStercobilinStercobilin is a tetrapyrrolic bile pigment and is one end-product of heme catabolism. It is the chemical responsible for the brown color of human fecal material and was originally isolated from feces in 1932...
- UrobilinUrobilinUrobilin is a yellow linear tetrapyrrole, resulting from the breakdown of heme, a cyclic tetrapyrrole.Urobilin is produced when Urobilinogen is oxidized by intestinal bacteria; it can also be...