Abstract
The X-ray structure of reaction centers (RCs) of R.viridis [1] and Rb.sphaeroides [2] has revealed that the only amino acid residue bridging between bacteriopheophytin (HA) and quinone (QA) at the active branch (A-branch) is tryptophane at the position M252 or M250, respectively. This aromatic amino acid residue is conserved in all the bacterial RCs sequenced so far including Rb.capsulatus as well as in photosystem II of plants. Due to its proximity to both H and QA TRP M250 could play a dual role as a stabilizer of the structure of the nearby cofactors and as a functional component of the protein, accelerating the electron transfer (ET) rate kQ from P+H<Stack><Subscript>A</Subscript><Superscript>−</Superscript></Stack> to P+Q<Stack><Subscript>A</Subscript><Superscript>−</Superscript></Stack> Molecular orbital calculations using the intermolecular overlap approximation and the atomic coordinates of R.viridis at 2.2 Angström resolution indeed support a predominant superexchange contribution to the electronic coupling between H<Stack><Subscript>A</Subscript><Superscript>−</Superscript></Stack>-QA and HĀ QA −[3].
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Coleman, W.J. et al. (1990). How Conclusive is Mutagenetic Replacement of TRP M250 in Photosynthetic Reaction Centers ?. In: Baltscheffsky, M. (eds) Current Research in Photosynthesis. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-0511-5_32
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DOI: https://doi.org/10.1007/978-94-009-0511-5_32
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