www.checkbiotech.org ; www.raupp.info ; www.czu.cz

Researchers from Freie Universität Berlin identify a new step in
photosynthesis, November 2005.

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 sunlight reaching them, and how they
transform it into other forms of energy. Researchers Michael Haumann and
Holger Dau, from the Freie Universität 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 converting 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 atom 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 the "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 with X-rays.

They flashed the sample with a laser and registered the change using X-ray
fluorescence every 10 microseconds to find out how different oxidation
states developed. When carefully analysing the reaction kinetics, they
observed a time delay before the O2-evolving step. This delay unambiguously
proved the existence of the long-searched for intermediate state.

How far away are we then from using the sun to power our daily lives?
Michael Haumann, the main author of the publication, asserts that "these are
important results that will make an impact in the photosynthesis community.
They help our understanding of how solar energy is used in plants and
contribute to the efforts to produce more efficient solar cells for our
needs".

[www.esrf.fr]

------------------------------------------
Posted to Phorum via PhorumMail