2004-01-13 19:46:00WuYung123
藻紅素筆記:
藻紅素筆記:
(MacColl, R. (1991))
There are two common types of phycoerythrins (R- and C-), which can be isolated from the organelles, phycobilisomes, on the outer surface of the thylakoid membranes of red alga and cyanobacterium respectively. The physobilisomes usually consisting of an allophycocyanin core and six rods, which contain phycocyanin and phycoerythrin.
Phycoerythrins are photosynthetic light-harvesting proteins, which transfer light energy with high efficiencies over relatively long distances to the photosynthetic reaction centre, which is the initial event of photosynthesis. Phycoerythrins possess the highest energy chromophores - phycoerythrobilins and, sometimes, phycourobilins. Photons captured by the chromophores are then migrated to the lowest energy chromophores on the same protein, then consecutively to other phycoerythrins, phycocyanins, allophycocyanins, and chlorophyll a-protein complexes. C-phycoerythrin is usually isolated as a hexameric (a6b6) protein aggregate have phycoerhthrin as its only chromophore, there there are five phycoerythrobilins on each (ab) monomer of an aggregate. The phycoerythrobilins can interact with the apoprotein and perhaps with each other to form different energy levels. R-phycoerythrin has both phycoerythrobilins and phycourobilins, and usually isolated as (a6b6r). The chromophores are linear tetrapyrroles and are covalently linked by one or two thioether bonds.
While C-phycoerythrin has an absorbance maxima at 540nm, R-phycoerythrin has two maxima and one pronounced shoulder at 494, 565 and 545nm respectively. The 494nm band was due to phycourobilin and the other two bands were different energetic states of phycoerythrobilin. The two highest-energy bands suggested that at least 2 sensitising chromophores were present. The emission spectrums of the two phycoerythrins were similar with one main band suggesting that energy migrated to the lowest-energy chromophores prior to emission. Since when each chromphore was isolated free of overlapping absorbance from other chromophores, they all exhibited single transitions in the visible region, therefore it is unlikely that a single chromphore might produce more than one visible absorption band. The energy transfer between pairs of chromophores was normally considered to be dipole-dipole coupling.
(MacColl, R. (1991))
There are two common types of phycoerythrins (R- and C-), which can be isolated from the organelles, phycobilisomes, on the outer surface of the thylakoid membranes of red alga and cyanobacterium respectively. The physobilisomes usually consisting of an allophycocyanin core and six rods, which contain phycocyanin and phycoerythrin.
Phycoerythrins are photosynthetic light-harvesting proteins, which transfer light energy with high efficiencies over relatively long distances to the photosynthetic reaction centre, which is the initial event of photosynthesis. Phycoerythrins possess the highest energy chromophores - phycoerythrobilins and, sometimes, phycourobilins. Photons captured by the chromophores are then migrated to the lowest energy chromophores on the same protein, then consecutively to other phycoerythrins, phycocyanins, allophycocyanins, and chlorophyll a-protein complexes. C-phycoerythrin is usually isolated as a hexameric (a6b6) protein aggregate have phycoerhthrin as its only chromophore, there there are five phycoerythrobilins on each (ab) monomer of an aggregate. The phycoerythrobilins can interact with the apoprotein and perhaps with each other to form different energy levels. R-phycoerythrin has both phycoerythrobilins and phycourobilins, and usually isolated as (a6b6r). The chromophores are linear tetrapyrroles and are covalently linked by one or two thioether bonds.
While C-phycoerythrin has an absorbance maxima at 540nm, R-phycoerythrin has two maxima and one pronounced shoulder at 494, 565 and 545nm respectively. The 494nm band was due to phycourobilin and the other two bands were different energetic states of phycoerythrobilin. The two highest-energy bands suggested that at least 2 sensitising chromophores were present. The emission spectrums of the two phycoerythrins were similar with one main band suggesting that energy migrated to the lowest-energy chromophores prior to emission. Since when each chromphore was isolated free of overlapping absorbance from other chromophores, they all exhibited single transitions in the visible region, therefore it is unlikely that a single chromphore might produce more than one visible absorption band. The energy transfer between pairs of chromophores was normally considered to be dipole-dipole coupling.