2 research outputs found
Functional Compartmental Modeling of the Photosystems in the Thylakoid Membrane at 77 K
Time-resolved
fluorescence spectroscopy measurements at 77 K on
thylakoid membrane preparations and isolated photosynthetic complexes
thereof were investigated using target analysis with the aim of building
functional compartmental models for the photosystems in the thylakoid
membrane. Combining kinetic schemes with different spectral constraints
enabled us to resolve the energy transfer pathways and decay characteristics
of the different emissive species. We determined the spectral and
energetic properties of the red Chl pools in both photosystems and
quantified the formation of LHCII-LHCI-PSI supercomplexes in the transition
from native to unstacked thylakoid membranes
Energy Transfer and Trapping in Red-Chlorophyll-Free Photosystem I from <i>Synechococcus</i> WH 7803
We
report for the first time steady-state and time-resolved emission
properties of photosystem I (PSI) complexes isolated from the cyanobacterial
strain <i>Synechococcus</i> WH 7803. The PSI complexes from
this strain display an extremely small fluorescence emission yield
at 77 K, which we attribute to the absence of so-called red antenna
chlorophylls, chlorophylls with absorption maxima at wavelengths longer
than those of the primary electron donor P700. Emission measurements
at room temperature with picosecond time resolution resulted in two
main decay components with lifetimes of about 7.5 and 18 ps and spectra
peaking at about 685 nm. Especially in the red flanks, these spectra
show consistent differences, which means that earlier proposed models
for the primary charge separation reactions based on ultrafast (∼1
ps) excitation equilibration processes cannot describe the data. We
show target analyses of a number of alternative models and conclude
that a simple model (Ant2)* ↔ (Ant1/RC)* → RP2 can explain
the time-resolved emission data very well. In this model, (Ant2)*
represents chlorophylls that spectrally equilibrate in about 7.5 ps
and in which RP2 represents the “final” radical pair
P700<sup>+</sup>A<sub>0</sub><sup>–</sup>. Adding an equilibrium
(Ant1/RC)* ↔ RP1, in which RP1 represents an “intermediate”
radical pair A<sup>+</sup>A<sub>0</sub><sup>–</sup>, resulted
in the same fit quality. We show that the simple model without RP1
can easily be extended to PSI complexes from cyanobacteria with one
or more pools of red antenna chlorophylls and also that the model
provides a straightforward explanation of steady-state emission properties
observed at cryogenic temperatures