"We initially thought this reaction center was non-functional," said Beatty. "We were forced to think in new ways to explain the surprising results, which led to some nice insight."
Lin carefully measured the light absorption spectra for the naturally occurring magnesium reaction center and compared it to the mutant reaction center that was replaced with zinc bacteriochlorophylls. She found that, though the zinc-coordinated reaction center is comprised of six bacteriochlorophylls, changing their structure to a configuration similar to that used in plant photosystem I reaction centers, surprisingly, the data from the reaction kinetics and the energy conversion efficiency were almost identical to the magnesium containing reaction center.
"Amazingly, the reaction center still works with essentially the same physical chemical properties as the normal system," said Neal Woodbury, deputy director of the Biodesign Institute. "This was a real puzzle when Su first did these measurements, but she was able to figure out why."
"The electron transfer driving force can be determined by either the properties of the metal cofactors themselves or through their interaction with the protein," said Lin. "In the case of the zinc reaction center, the driving force is regulated through the coordination of the metal."
"Once again, biology shows its resilience so that changes in one area are compensated by changes in others and the protein's ability to dynamically adjust," said Woodbury.
The results may enable researchers to explore a deeper understanding of the structure, function, and evolution of photosynthesis reaction centers in photosystems I and II. Of particular interest, are studies that focus on the interaction between chlorophylls and protein, which differs in naturally occurring reaction center variants.
The team may also
|Contact: Joe Caspermeyer|
Arizona State University