Ultrafast primary processes in PS I from Synechocystis sp. PCC 6803: roles of P700 and A(0).
The excitation transport and trapping kinetics of core antenna-reaction center complexes from photosystem I of wild-type Synechocystis sp. PCC 6803 were investigated under annihilation-free conditions in complexes with open and closed reaction centers. For closed reaction centers, the long-component decay-associated spectrum (DAS) from global analysis of absorption difference spectra excited at 660 nm is essentially flat (maximum amplitude <10(-5) absorbance units). For open reaction centers, the long-time spectrum (which exhibits photobleaching maxima at approximately 680 and 700 nm, and an absorbance feature near 690 nm) resembles one previously attributed to (P700(+) - P700). For photosystem I complexes excited at 660 nm with open reaction centers, the equilibration between the bulk antenna and far-red chlorophylls absorbing at wavelengths >700 nm is well described by a single DAS component with lifetime 2.3 ps. For closed reaction centers, two DAS components (2.0 and 6.5 ps) are required to fit the kinetics. The overall trapping time at P700 ( approximately 24 ps) is very nearly the same in either case. Our results support a scenario in which the time constant for the P700 --> A(0) electron transfer is 9-10 ps, whereas the kinetics of the subsequent A(0) --> A(1) electron transfer are still unknown.
Savikhin
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S
Ames Laboratory, U. S. Department of Energy, Ames, Iowa 50011, USA.
Xu
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W
Chitnis
P R
PR
Struve
W S
WS
D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism*; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000502:physiology*; D007700:Kinetics; D008958:Models, Molecular; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D013053:Spectrophotometry
D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll; C001785:chlorophyll P 700; D000077194:Chlorophyll A