Light-harvesting complex

[3] Light-harvesting complexes are found in a wide variety among the different photosynthetic species, with no homology among the major groups.

Photosynthesis is a process where light is absorbed or harvested by pigment protein complexes which are able to turn sunlight into energy.

Carotenoids are long linear organic molecules that have alternating single and double bonds along their length.

The antenna-shaped light harvesting complex of cyanobacteria, glaucocystophyta, and red algae is known as the phycobilisome which is composed of linear tetrapyrrole pigments.

Pigment-protein complexes referred to as R-phycoerythrin are rod-like in shape and make up the rods and core of the phycobilisome.

The pigments, such as phycocyanobilin and phycoerythrobilin, are the chromophores that bind through a covalent thioether bond to their apoproteins at cystein residues.

They enhance the amount and spectral window of light absorption and fill the "green gap", which occurs in higher plants.

This increases the surface area of the absorbing section and helps focus and concentrate light energy down into the reaction center to form chlorophyll.

The energy transfer from excited electrons absorbed by pigments in the phycoerythrin subunits at the periphery of these antennas appears at the reaction center in less than 100 ps.