Using sunlight to power our homes and offices is an unaccomplished dream due to the still inefficient technology for a better use of solar energy. The study of photosynthesis in plants could provide new clues by explaining how they absorb almost 100% of the sun-light reaching them, and how they transform it into other forms of energy. Researchers Michael Haumann and Holger Dau, from the Freie Universitt Berlin, used the X-ray source of the European Synchrotron Radiation Facility (ESRF) to investigate the kinetics of the photosynthesis process. They have confirmed the existence of a fifth step in the catalysis process of water into oxygen, and have published their results in Science.

Chlorophyll in plants absorbs light from the sun, which then becomes energy used by the so-called "oxygen-evolving complex" to catalyse the splitting of water into molecular oxygen. This complex contains four manganese and one calcium atoms that are known to be at the centre of the catalytic reaction. Five intermediate states have been proposed in the process of photosynthesis - a cycle known as "Kok cycle"- but only four had been proved until recently. With the help of the ESRF, scientists have been able to identify the missing state, which is particularly important because it is directly involved in the molecular oxygen formation. They suggest, furthermore, an extension of the "Kok cycle" with an additional intermediate and propose a new reaction mechanism on a molecular basis for the release of dioxygen. This gives new insight into the mechanism of photosynthesis.

In order to study this process, the use of synchrotron light was crucial: "A very intense and stable X-ray beam is necessary to perform this study on such a complex, highly diluted protein present in the investigated spinach sample", explains Pieter Glatzel, head of beamline ID26, where the experiments were carried out. The researchers measured the fluorescence from the sample that is emitted after excitation
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Contact: Montserrat Capellas
capellas@esrf.fr
33-476-88-26-63
European Synchrotron Radiation Facility
28-Nov-2005

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