Phycourobilin
Encyclopedia
Phycourobilin is a tetrapyrrole
orange molecule involved in photosynthesis
in cyanobacteria and red algae. This chromophore is bound to the phycobiliprotein
phycoerythrin
, the distal component of the light-harvesting system of cyanobacteria and red algae (phycobilisome
).
When bound to phycoerythrin
, phycourobilin shows an absorption maximum around 495 nm. This chromophore is always a donor chromophore of phycoerythrin
s, since their acceptor chromophore is always phycoerythrobilin
. It can also be linked to the linker polypeptides of the phycobilisome
, in which its precise role remains unclear.
Phycourobilin is found in marine phycobilisome
containing organisms, allowing them to efficiently absorb blue-green light. In the ubiquitous marine cyanobacteria Synechococcus
, the amount of phycourobilin in the phycobilisome
s is correlated to the ecological niche the cells inhabit: offshore Synechococcus
are quite phycourobililin-rich, while coastal Synechococcus
contain very little or no phycourobilin. This represents a remarkable adaptation of the cyanobacterial light-harvesting system, as oceanic waters are relatively richer in blue light than onshore waters.
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...
orange molecule involved in photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
in cyanobacteria and red algae. This chromophore is bound to the phycobiliprotein
Phycobiliprotein
Phycobiliproteins 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...
phycoerythrin
Phycoerythrin
Phycoerythrin is a red protein from the light-harvesting phycobiliprotein family, present in cyanobacteria, red algae and cryptomonads.Like all phycobiliproteins, phycoerythrin is composed of a protein part, organised in a hexameric structure of alpha and beta chains, covalently binding...
, the distal component of the light-harvesting system of cyanobacteria and red algae (phycobilisome
Phycobilisome
Phycobilisomes are light harvesting antennae of photosystem II in cyanobacteria, red algae and glaucophytes.- General structure :Phycobilisomes are protein complexes anchored to thylakoid membranes. They are made of stacks of chromophorylated proteins, the phycobiliproteins, and their associated...
).
When bound to phycoerythrin
Phycoerythrin
Phycoerythrin is a red protein from the light-harvesting phycobiliprotein family, present in cyanobacteria, red algae and cryptomonads.Like all phycobiliproteins, phycoerythrin is composed of a protein part, organised in a hexameric structure of alpha and beta chains, covalently binding...
, phycourobilin shows an absorption maximum around 495 nm. This chromophore is always a donor chromophore of phycoerythrin
Phycoerythrin
Phycoerythrin is a red protein from the light-harvesting phycobiliprotein family, present in cyanobacteria, red algae and cryptomonads.Like all phycobiliproteins, phycoerythrin is composed of a protein part, organised in a hexameric structure of alpha and beta chains, covalently binding...
s, since their acceptor chromophore is always phycoerythrobilin
Phycoerythrobilin
Phycoerythrobilin 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...
. It can also be linked to the linker polypeptides of the phycobilisome
Phycobilisome
Phycobilisomes are light harvesting antennae of photosystem II in cyanobacteria, red algae and glaucophytes.- General structure :Phycobilisomes are protein complexes anchored to thylakoid membranes. They are made of stacks of chromophorylated proteins, the phycobiliproteins, and their associated...
, in which its precise role remains unclear.
Phycourobilin is found in marine phycobilisome
Phycobilisome
Phycobilisomes are light harvesting antennae of photosystem II in cyanobacteria, red algae and glaucophytes.- General structure :Phycobilisomes are protein complexes anchored to thylakoid membranes. They are made of stacks of chromophorylated proteins, the phycobiliproteins, and their associated...
containing organisms, allowing them to efficiently absorb blue-green light. In the ubiquitous marine cyanobacteria Synechococcus
Synechococcus
Synechococcus is a unicellular cyanobacterium that is very widespread in the marine environment. Its size varies from 0.8 µm to 1.5 µm...
, the amount of phycourobilin in the phycobilisome
Phycobilisome
Phycobilisomes are light harvesting antennae of photosystem II in cyanobacteria, red algae and glaucophytes.- General structure :Phycobilisomes are protein complexes anchored to thylakoid membranes. They are made of stacks of chromophorylated proteins, the phycobiliproteins, and their associated...
s is correlated to the ecological niche the cells inhabit: offshore Synechococcus
Synechococcus
Synechococcus is a unicellular cyanobacterium that is very widespread in the marine environment. Its size varies from 0.8 µm to 1.5 µm...
are quite phycourobililin-rich, while coastal Synechococcus
Synechococcus
Synechococcus is a unicellular cyanobacterium that is very widespread in the marine environment. Its size varies from 0.8 µm to 1.5 µm...
contain very little or no phycourobilin. This represents a remarkable adaptation of the cyanobacterial light-harvesting system, as oceanic waters are relatively richer in blue light than onshore waters.