Melih K. Sener, Deyu Lu, Thorsten Ritz, Sanghyun Park, Petra Fromme, and
Klaus Schulten.
Robustness and optimality of light harvesting in cyanobacterial
photosystem I.
Journal of Physical Chemistry B, 106:7948-7960, 2002.
SENE2002A
As most biological species, photosynthetic lifeforms have evolved
to function optimally, despite thermal disorder and with fault
tolerance. It remains a challenge to understand how this is
achieved. To address this challenge the function of the protein-
pigment complex photosystem I (PSI) of the cyanobacterium
Synechococcus elongatus is investigated theoretically. The
recently obtained high resolution structure of this complex exhibits
an aggregate of 96 chlorophylls that are electronically coupled to
function as a light-harvesting antenna complex. This paper
constructs an effective Hamiltonian for the chlorophyll aggregate
to describe excitation transfer dynamics and spectral properties of
PSI. For this purpose, a new kinetic expansion method, the
sojourn expansion, is introduced. Our study shows that at room
temperature fluctuations of site energies have little effect on the
calculated excitation lifetime and quantum yield, which compare
favorably with experimental results. The efficiency of the system is
found to be robust against `pruning' of individual chlorophylls.
An optimality of the arrangement of chlorophylls is identified
through the quantum yield in comparison with an ensemble of
randomly oriented chlorophylls, though, the quantum yield is seen
to change only within a narrow interval in such an ensemble.
