Phycobilisome


Phycobilisome

Phycobilisomes are light harvesting antennae of photosystem II in cyanobacteria, red algae and glaucophytes.

General structure

Phycobilisomes are protein complexes (up to 600 polypeptides) anchored to thylakoid membranes. They are made of stacks of chromophorylated proteins, the phycobiliproteins, and their associated linker polypeptides. Each phycobilisome consists of a core made of allophycocyanin, from which several outwardly oriented rods made of stacked disks of phycocyanin and (if present) phycoerythrin(s) or phycoerythrocyanin. The spectral property of phycobiliproteins are mainly dictated by their prosthetic groups, which are linear tetrapyrroles known as phycobilins including phycocyanobilin, phycoerythrobilin, phycourobilin and phycobiliviolin. The spectral properties of a given phycobilin is influenced by its protein environment.

Function

Each phycobiliprotein has a specific absorption and fluorescence emission maximum in the visible range of light. Therefore, their presence and the particular arrangement within the phycobilisomes allow absorption and unidirectional transfer of light energy to chlorophyll "a" of the photosystem II. In this way, the cells take advantage of the available wavelengths of light (in the 500-650 nm range), which are inaccessible to chlorophyll, and utilize their energy for photosynthesis. This is particularly advantageous deeper in the water column, where light with longer wavelengths is less transmitted and therefore less available directly to chlorophyll.

The geometrical arrangement of a phycobilisome is very elegant and results in 95% efficiency of energy transfer.

Evolution and diversity

There are many variations to the general phycobilisomes structure. Their shape can be hemidiscoidal (in cyanobacteria) or hemiellipsoidal (in red algae).

The phycobiliproteins themselves show little sequence evolution due to their highly constrained function (absorption and transfer of specific wavelengths). In some species of cyanobacteria, when both phycocyanin and phycoerythrin is present, the phycobilisome can undergo significant restructuring as response to light color. In green light the distal portions of the rods are made of red colored phycoerythrin, which absorbs green light better. In red light, this is replaced by blue colored phycocyanin, which absorbs red light better. This reversible process is known as complementary chromatic adaptation.

External links

*


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Phycobilisome — Le phycobilisome est un complexe collecteur d énergie lumineuse de l appareil photosynthétique présent chez les Cyanobacteria et des Rhodophyta ainsi que les Glaucocystophyta. Il est extrinsèque à la membrane thylakoïdale et constitué de… …   Wikipédia en Français

  • phycobilisome — An accessory light energy harvesting structure in cyanobacteria. They have cores of allophycocyanin with radiating rods composed of discs of phycocyanin and phycoerythrin. Linker polypeptides attach the core to the thylakoid membranes. These… …   Dictionary of molecular biology

  • phycobilisome — noun A light harvesting antenna in cyanobacteria, red algae and glaucophytes …   Wiktionary

  • phycobilisome — …   Useful english dictionary

  • Фикобилисомы — Модель расположения белковых субъединиц в фикобилисоме (полудисковидный тип) Белки фик …   Википедия

  • Light-harvesting complex — A light harvesting complex is one or more polypeptide chains containing photosynthetic pigments, which surrounds a photosynthetic reaction centre and focuses energy, attained from photons absorbed by the pigment, inward toward the reaction centre …   Wikipedia

  • Phycourobilin — Chembox new ImageFile=phycourobilin.png ImageSize=200px IUPACName=3 [2 [( Z ) [3 (2 carboxyethyl) 5 [ [( 2R ) 4 ethyl 3 methyl 5 oxo 1,2 dihydropyrrol 2 yl] methyl] 4 methyl 2 pyrrolylidene] methyl] 5 [ [( 2S ) 3 ethyl 4 methyl 5 oxo 1,2… …   Wikipedia

  • Orange carotenoid N-terminal domain — Carot N crystal structure of orange carotenoid protein Identifiers Symbol Carot N Pfam …   Wikipedia

  • Photosynthesis — Composite image showing the global distribution of photosynthesis, including both oceanic phytoplankton and vegetation …   Wikipedia

  • Cyanobacteria — Temporal range: 3500–0 Ma Had n Archean …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.