Resolution of low-energy chlorophylls in Photosystem I of Synechocystis sp. PCC 6803 at 77 and 295 K through fluorescence excitation anisotropy |
| |
Authors: | Vincent M Woolf Bruce P Wittmershaus Wim F J Vermaas Trung D Tran |
| |
Institution: | (1) Department of Physics and Astronomy, Arizona State University, 85287 Tempe, AZ, USA;(2) Department of Botany, Arizona State University, 85287 Tempe, AZ, USA;(3) the Center for the Study of Early Events in Photosynthesis, Arizona State University, 85287 Tempe, AZ, USA;(4) Present address: Department of Astronomy, University of Texas at Austin, 78712 Austin, TX, USA |
| |
Abstract: | Fluorescence excitation spectra of highly anisotropic emission from Photosystem I (PS I) were measured at 295 and 77 K on a PS II-less mutant of the cyanobacterium Synechocystis sp. PCC 6803 (S. 6803). When PS I was excited with light at wavelengths greater than 715 nm, fluorescence observed at 745 nm was highly polarized with anisotropies of 0.32 and 0.20 at 77 and 295 K, respectively. Upon excitation at shorter wavelengths, the 745-nm fluorescence had low anisotropy. The highly anisotropic emission observed at both 77 and 295 K is interpreted as evidence for low-energy chlorophylls (Chls) in cyanobacteria at room temperature. This indicates that low-energy Chls, defined as Chls with first excited singlet-state energy levels below or near that of the reaction center, P700, are not artifacts of low-temperature measurements.If the low-energy Chls are a distinct subset of Chls and a simple two-pool model describes the excitation transfer network adequately, one can take advantage of the low-energy Chls' high anisotropy to approximate their fluorescence excitation spectra. Maxima at 703 and 708 nm were calculated from 295 and 77 K data, respectively. Upper limits for the number of low-energy Chls per P700 in PS I from S. 6803 were calculated to be 8 (295 K) and 11 (77 K).Abbreviations Chl -
chlorophyll
- BChl -
bacteriochlorophyll
- LHC -
light-harvesting chlorophyll
- PS -
Photosystem
- RC -
reaction center
-
S. 6803 -
Synechocystis sp. PCC 6803 |
| |
Keywords: | anisotropy cyanobacteria fluorescence low-energy chlorophyll Photosystem I temperature dependence |
本文献已被 SpringerLink 等数据库收录! |
|