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The enigmatic cytochrome b‐559 of oxygenic photosynthesis
Author(s) -
Cramer William A.,
Tae GunSik,
Furbacher Paul N.,
Böttger Michel
Publication year - 1993
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1993.tb01392.x
Subject(s) - cytochrome b6f complex , cytochrome , photosynthetic reaction centre , electron transport chain , cytochrome c1 , cytochrome b , photosynthesis , redox , heme , photosystem i , chemistry , cytochrome f , cytochrome c , photosystem ii , biophysics , photochemistry , coenzyme q – cytochrome c reductase , biology , biochemistry , mitochondrion , inorganic chemistry , mitochondrial dna , gene , enzyme
The ubiquitous and obligatory association of cytochrome b ‐559 with the photosystem II reaction center of oxygenic photosynthesis is a conundrum since it seems not to have a function in the primary electron transport pathway of oxygen evolution. A model for the cytochrome structure that satisfies the cis ‐positive rule for membrane protein assembly consists of two short, non‐identical hydrophobic membrane‐spanning polypeptides (α and β), each containing a single histidine residue, as ligands for the bridging heme prosthetic group that is on the side of the membrane opposite to the water splitting apparatus. The ability of the heterodimer, but not the single α‐subunit, to satisfy the cis ‐positive rule implies that the cytochrome inserts into the membrane as a heterodimer, with some evidence implicating it as the first membrane inserted unit of the assembling reaction center. The very positive redox potential of the cytochrome can be explained by a position for the heme in a hydrophobic niche near the stromal aqueous interface where it is also influenced by the large positive dipole potential of the parallel α‐helices of the cytochrome. The requirement for the cytochrome in oxygenic photosynthesis may be a consequence of the presence of the strongly oxidizing reaction center needed for H 2 O‐splitting. This may lead to the need, under conditions of stress or plastid development, for an alternate source of electrons when the H 2 O‐splitting system is not operative as a source of reductant for the reaction center.