Electron Transport to Photosystem I by Soluble Carriers: Evolution of the Interacting Pair

Oxygenic photosynthesis is driven via sequential action of Photosystem II (PSII) and (PSI) reaction centers via the Z-­‐scheme. Both of these pigment– membrane protein complexes are found in cyanobacteria, algae, and plants. PSI, unlike PSII, is remarkably stable and does not undergo limiting photo-­‐damage. This stability, as well as other fundamental structural differences, makes PSI the most attractive reaction centers for applied photosynthetic applications. These applied applications exploit the efficient light harvesting and high quantum yield of PSI where the isolated PSI particles are redeployed providing electrons directly as a photocurrent or, via a coupled catalyst to yield H2. Here, we explore the reduction rate of photo-­‐oxidized PSI with various natural and artificial electron donors. The electron transfer rate from various donors to oxidized PSI has been measured for a wide range of photosynthetic organisms encompassing cyanobacteria, algae, and plants, mainly by transient absorption spectroscopy. We utilize a Joliot-­‐type, LED-­‐ driven, pump-­‐probe spectrometer, along with molecular biology, genomics, and bioinformatics approaches to further investigate the relationship of this ever-­‐ evolving interacting pair with their electron transfer rates. We also implement our expanding biochemistry toolkit in hopes to increase this rate for applied photosynthesis applications, where it has become a bottle-­‐neck for many bio-­‐energy related bio-­‐hybrid devices.