What governs the reaction center excitation wavelength of photosystems I and II?
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The sun’s spectrum harvested through photosynthesis is the primary source of energy for life on earth. Plants, green algae, and cyanobacteria—the major primary producers on earth—utilize reaction centers that operate at wavelengths of 680 and 700 nm. Why were these wavelengths “chosen” in evolution? This study analyzes the efficiency of light conversion into chemical energy as a function of hypothetical reaction center absorption wavelengths given the sun’s spectrum and the overpotential cost associated with charge separation. Surprisingly, it is found here that when taking into account the empirical charge separation cost the range 680–720 nm maximizes the conversion efficiency. This suggests the possibility that the wavelengths of photosystem I and II were optimized at some point in their evolution for the maximal utilization of the sun’s spectrum.
KeywordsReaction center Optimality Spectrum Efficiency Chlorophyll
Reaction center excitation energy
The author thanks Eran Bouchbinder for generous help with the thermodynamic analysis and Michael Brenner, William Parson, Robert Knox, John Bolton, Govindjee, Mary Archer, Marc Kirschner, Mike Springer, Sallie Chisholm, Bernhard Loll, Jacques Dumais, Deepak Barua, and Rafael Rubio de Casas for helpful discussions of the analysis and manuscript.
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