But until now, the precise structure of the catalyst has eluded all attempts of determination by x-ray diffraction and various spectroscopic techniques. Even a 3.0-ngstrom-resolution structure obtained by the Berkeley Lab group's collaborators at the Technical and Free Universities in Berlin, using x-ray diffraction, didn't allow the researchers to pinpoint the exact positions of the cluster's manganese and calcium atoms and its surrounding ligands. Part of the problem is the fact that the metal catalyst is highly susceptible to radiation damage, which rules out extremely high-resolution x-ray diffraction studies.
To minimize radiation damage, Yano and colleagues combined x-ray absorption fine structure spectroscopy measurements with x-ray diffraction data from crystallographic studies, which were obtained at the Stanford Synchrotron Radiation Laboratory, where the techniques used in this study were developed in collaboration with the Berkeley Lab scientists. This technique exposes the Mn4Ca cluster to much lower doses of radiation, and enabled the team to obtain three similar structures at a resolution much higher than previously possible.
These three structures shed new light on how the catalyst fits within the much larger photosystem II protein complex. The x-ray diffraction structures at a medium resolution are sufficient to determine the overall shape and placement of the catalyst within the protein complex, and the spectroscopy measurements provide high-resolu
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Contact: Dan Krotz
dakrotz@lbl.gov
510-486-4019
DOE/Lawrence Berkeley National Laboratory
3-Nov-2006