Kinetic Analysis of the Thermal Stability of the Photosynthetic Reaction Centre from Rhodobacter sphaeroides
Arwel V Hughes 1*, Paul Rees 2, Peter Heathcote 3 and Michael R Jones 4
1 Rutherford Appleton Laboratory
2 Swansea University
3 Queen Mary University, London
4 University of Bristol School of Medical Sciences
* To whom correspondence should be addressed. E-mail: a.v.hughes{at}rl.ac.uk.
Submitted on August 10, 2005
Revised on September 27, 2005
Accepted on 19 January 2006
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Abstract |
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The temperature-induced denaturation of the photosynthetic reaction centre from Rhodobacter sphaeroides has been studied through the changes that occur in the absorption spectrum of the bound chromophores on heating. At elevated temperatures the characteristic absorbance bands of the bacteriochlorins bound to the polypeptides within the reaction centre are lost, and are replaced by features typical of unbound bacteriochlorophyll and bacteriopheophytin. The kinetics of the spectral changes cannot be explained by a direct conversion from the functional to the 'denatured' form of the protein, and require the presence of at least one intermediate. Possible mechanisms for the transformation via an intermediate are examined using a global analysis of the kinetic data, and the most likely mechanism is shown to involve a reversible transformation between the native state and an off-pathway intermediate, coupled to an irreversible transformation to the denatured state. The activation energies for the transformations between the three components are calculated from the effect of temperature on the individual rate constants, and the likely structural changes of the protein during the temperature-induced transformation are discussed.
Key Words:
Lipid bilayer, Membrane protein, Photosynthesis, thermal stability
