ODMR spectroscopy of molecular functions in photosynthetic membrane proteins

For the last twenty years, in our laboratory in Padova, we have been studying photosynthetic membrane proteins by optically detected magnetic resonance (ODMR), a spectroscopic tool very suitable to detect characteristics and features of the pigments in their triplet state. These studies parallel the epochal development of membrane protein single-crystal X-ray analysis, started in 1984, of which George Feher was a pioneer. Structural knowledge was a new starting point in asking the proper questions related to the functioning of reaction centers and light-harvesting complex proteins, unique to photosynthesis, and spectroscopists of all kinds found new enlightenment in their searches for function details. The first part of this review will be devoted to describe the molecular species which may be observed by ODMR and explain its principle and why it is a useful and powerful technique in the study of photosynthetic proteins. The second part will illustrate some examples of the functional mechanisms which can be revealed, especially in cases where one is able to look at systems which are among the more complex of those whose structures have been studied. We mean integrated systems where both the reaction centers and the light-harvesting complexes are present in their natural and mutual relationship within the large physiological membrane.

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