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Updated: Apr 27, 2026

Improving High Viscosity Extrusion of Microcrystals for Time-resolved Serial Femtosecond Crystallography at X-ray Lasers
Published on: February 28, 2019
Taking snapshots of photosynthetic water oxidation using femtosecond X-ray diffraction and spectroscopy
Jan Kern1, Rosalie Tran2, Roberto Alonso-Mori3
11] Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [2] LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
Abstract:
The dioxygen we breathe is formed by light-induced oxidation of water in photosystem II. O2 formation takes place at a catalytic manganese cluster within milliseconds after the photosystem II reaction centre is excited by three single-turnover flashes. Here we present combined X-ray emission spectra and diffraction data of 2-flash (2F) and 3-flash (3F) photosystem II samples, and of a transient 3F' state (250 μs after the third flash), collected under functional conditions using an X-ray free electron laser. The spectra show that the initial O-O bond formation, coupled to Mn reduction, does not yet occur within 250 μs after the third flash. Diffraction data of all states studied exhibit an anomalous scattering signal from Mn but show no significant structural changes at the present resolution of 4.5 Å. This study represents the initial frames in a molecular movie of the structural changes during the catalytic reaction in photosystem II.
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