To get a closer look at what was happening during photosynthesis, the team used a well studied purple photosynthetic bacterium called Rhodobacter sphaeroides. This type of organism was likely one of the earliest photosynthetic bacteria to evolve. The researchers focused their efforts by studying the center stage of photosynthesis, the reaction center, where light energy is funneled into specialized chlorophyll binding proteins.
The textbook picture of photosynthesis represents the reaction center proteins as a scaffold, holding chlorophyll molecules at a highly optimized distance and orientation so that electrons can hop from one chlorophyll to another. With the chlorophylls in just the right position, any systematic protein movement was thought to be merely a side product of electrons shuttling between chlorophyll molecules.
Sudipa is collaborating with the Photosynthetic Antenna Research Center (PARC), one of DOE’s Energy Frontier Research Centers, to understand the basic scientific principles that underpin photosynthetic antenna complexes. These complexes are responsible for gathering energy from light.
One of the goals of the PARC is to find ways to expand an antenna’s spectral range to process more sunlight, in turn producing more fixed carbon that could be converted to fuel. Algae, for example, produce oils and fats during the photosynthesis process, and these materials can be converted into biodiesel. Increased production of oils and fats corresponds to larger amounts of biodiesel.
Photosynthesis should make any short-list of Nature’s spectacular accomplishments. Through the photosynthetic process, green plants and cyanobacteria are able to transfer energy from sunlight and initiate its conversion into chemical energy with an efficiency of nearly 100-percent. If we can learn to emulate Nature’s technique and create artificial versions of photosynthesis, then we, too, could effectively tap into the sun as a clean, efficient, sustainable and carbon-neutral source of energy for our technology.
“FMO is a model system for studying energy transfer in the photosynthetic process because it is relatively simple (consisting of only seven pigment molecules) and its chemistry has been well characterized,” Fleming said.
“This technique should also be useful in studies aimed at improving the efficiency of molecular solar cells,” Fleming said. In the Nature paper, he and his colleagues describe how they successfully used 2-D electronic spectroscopy to record the first direct measurement of electronic couplings in the Fenna-Matthews-Olson (FMO) photosynthetic light-harvesting protein, a molecular complex in green sulphur bacteria that absorbs photons and directs the excitation energy to a reaction center where it can be converted to chemical energy.
“As in all photosynthetic systems, the conversion of light into chemical energy is driven by electronic couplings between molecules and we monitored the process as a function of time and frequency.”
Emulating natural photosynthesis will require a better understanding of how energy gets transferred from light-absorbing pigment molecules to the molecules that make up the energy-converting reaction centers. Since the extra energy being transferred from one molecule to the next changes the way each absorbs and emits light, the flow of energy can be followed through optical spectroscopy, resolved on a femtosecond timescale.
IMAGE: The structure of the L and M subunits of the photosynthetic reaction center from Rhodobacter sphaeroides (based on PDB entry 1PCR). Theprotein is represented in purple, the cofactors are...
During the remarkable cascade of events of photosynthesis, plants approach the pinnacle of stinginess by scavenging nearly every photon of available light energy to produce food. Yet after many years of careful research into its exact mechanisms, some key questions remain about this fundamental biological process that supports all life on earth.
Now, a large research team led by Neal Woodbury, a scientist at ASU's Biodesign Institute, has come up with a new insight into the mechanism of photosynthesis, which involves the orchestrated movement of proteins on the timescale of a millionth of a millionth of a second. Their findings are described in "Protein Dynamics Control the Kinetics of Initial Electron Transfer in Photosynthesis," in the May 4 issue of Science.
“This gives us a new way to think about the design of artificial photosynthesis systems,” Fleming said. “It tells us that we must take into consideration the combined spatial-energetic arrangement of molecules in a system. If the molecules in a system are properly arranged in both space and energy, we can transport energy from one place to another much more efficiently.”
Sudipa, who earned a master’s in biochemistry and molecular biology from Wayne State University School of Medicine in Michigan, is exploring photosynthesis as part of , which is administered by the Oak Ridge Institute for Science and Education (ORISE) for the U.S. Department of Energy.