Protein Enables Discovery Of Quantum Effect In Photosynthesis

Science Daily When it comes to studying energy transfer in photosynthesis, it’s good to think “outside the bun.” That’s what Robert Blankenship, Ph.D., professor of biology and chemistry in Arts & Sciences at Washington University in St. Louis, did when he contributed a protein to a study performed by his collaborators at Lawrence Berkeley National Laboratory and the University of California at Berkeley.

Taco shell protein

It’s called bacteriochlorophyl (BChl) a protein, but Blankenship fondly calls it the taco shell protein because of its structure: its ribbon-like backbone wraps around three clusters of seven chlorophylls, just like a taco shell around ground beef. The structure also is referred to as trimeric because of the three clusters.

The protein, which comes from a photosynthetic bacterium that lives in extremely high temperatures, enabled the researches to discover that quantum mechanical effects appear to play a role in photosynthesis.

The taco shell protein is arguably the most studied and understood protein in a complex photosynthesis researchers refer to as the antenna system, molecules that efficiently transfer energy from light in a cascade.

Photosynthesis transforms light, carbon dioxide and water into chemical energy in plants and some bacteria. The wavelike characteristic of this energy transfer process can explain its extreme efficiency, in that vast areas of phase space can be sampled effectively to find the most efficient path for energy transfer.

“We have a very detailed molecular structure of this protein and we understand the electronic properties of it very well, too,” said Blankenship. “It’s taught us a lot about how chlorophylls interact with proteins. It was ideal for this study.”

Blankenship’s colleague, Graham R. Fleming, Ph.D., deputy director of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and professor of chemistry at the University of California, and colleagues used 2-D spectroscopy to study what happens inside a bacteriochlorophyll complex, and detected a ‘quantum beating.”

The effect, described in the April 12, 2007, issue of Nature, occurs when light-induced excitations in the complex meet and interfere constructively, much like the interactions that occur between the ripples formed by throwing stones into a pond.

The collaboration is a good illustration of interdisciplinary science. The Washington University group’s expertise is in photosynthesis, especially antenna systems, and the West Coast group’s specialty is advanced laser techniques. The quantum finding would have been impossible without collaboration.

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