"In an earlier study at the LCLS, we reported combined XRD and XES data from photosystem II samples in the dark S1 state and the one visible-flash illuminated S2 (1-flash) state," says Junko Yano, a chemist also with Berkeley Lab's Physical Biosciences Division and also a leader of this research. "In this new study we report data from the S3 (2-flash) and S0 (3-flash) states, which are the intermediate states directly before and after the evolution of the oxygen molecule. In addition, we report data for the first time from a light-induced transient state between the S3 and S0 states, which opens the window for elucidating the mechanism of oxygen-oxygen bond formation that occurs between these two states."
XRD data of all the flash states studied revealed an anomalous diffraction signal from Mn that is not complicated by signals from the overall protein matrix of carbon, nitrogen, oxygen and other metals, or even by the Ca atom, which is a part of the five atom Mn4Ca metalloenzyme complex.
"The detection of this anomalous Mn scattering signal not only validates the quality of our data, but also the procedures used for analyzing the data," says computational scientist Nicholas Sauter. Sauter and Paul Adams, both with Berkeley Lab's Physical Biosciences Division and both contributors to this study, are leading an effort to develop methods for analyzing data from the LCLS.
Yachandra and Yano believe that the detection of an anomalous Mn scattering signal opens up the possibility for detecting changes pertaining only to the Mn cluster as it advances through the S-state cycles and the oxygen-oxygen bond formation, which is where the ca
|Contact: Lynn Yarris|
DOE/Lawrence Berkeley National Laboratory