| Popis: |
Phycobilisomes (PBS) are highly efficient accessory light harvesting protein complexes, responsible for the conduction of light towards the photosynthetic reaction centers. They are exclusive for red algae, cyanobacteria and cryptophyta. Phycobiliproteins (PBP) are the main components of phycobilisomes and they contain bilin chromophores, tetrapyrrols in extended conformation, bound by a thioester bond to cysteines. PBPs have been classified by their spectroscopic properties as Allophycocyanin in the core of the complex (APC, Lambda max 651 nm), from where radiate rods formed by Phycoerythrin, (PE, Lambda max 565 nm) and Phycocyanin (PC,Lambda max 621 nm) (5, 12, 13). Phycobiliproteins in general are formed by heterodimers of alpha and beta subunits and are organized as trimers or hexamersPhycoerythrin (Chromophores: 1 Urobilin, 4 Erythrobilin per heterodimer) and Phycocyanin ( Chromophores: 3 cyanobilins per heterodimer) have been identified as a the phycobiliproteins present in the rods of the phycobilisome of Gracilaria chilensis. To study the energy transfer through a rod formed by two hexamers of phycoerythrin (ID=1eyx) and two hexamers of phycocyanin (ID=2bv8), the spectroscopic parameters of Phycourobilin and Erythrobilin were determined. In this report the quantum yield, half life were determined for hexameric PE, for the alfa and beta subunits and for purified chromophorylated proteolytic fragments form each subunit.Using this information and the values for Cyanobilin, the dipolar moments of each chromophore was calculated, as well as the orientation factor between pairs donor acceptor.The donor acceptor transfer constants using the extended Foster equation for the energy transfer in resonance, were calculated. Using a docking model for a rod, a main pathway for the light transfer in a rod is proposed. |
