Chapter 6 The Enigmatic Chlorophyll a Molecule in the Cytochrome b6f Complex
The structure of the cytochrome b 6 f complex, which functions in the “dark” reactions of oxygenic photosynthesis contains two pigment molecules, one molecule of chlorophyll a and β-carotene whose functions are not clear. It is proposed that the function of (a) the chlorophyll is to sense the passage of plastoquinone/quinol and, through close contact with a trans-membrane α-helix of the b 6 f subunit IV, to induce trans-membrane conformational changes dependent upon the PQ/PQH2 redox state. (b) It is proposed that the β-carotene has two functions: (i) situated 14 Å from the chlorophyll, it can exert its classical function of quenching the excited triplet state of the chlorophyll through an unprecedented mechanism proposed to involve long distance diffusion of singlet oxygen; (ii) inserted through the peripheral picket fence structure at the periphery of the b 6 f complex, β-carotene exerts a toothpick-like function in the assembly of the complex.
KeywordsAromatic Residue Excited Triplet State Oxygenic Photosynthesis Porphyrin Ring Pigment Molecule
high performance liquid chromatography
The studies described in this article were supported by grants from the NIH GM-038323 (W. A. C.) and NSF MCB-0516939 (S. S.).
Note: Literature survey completed 12/24/08.
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