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The cytochrome b 6 f complex. Novel aspects
Author(s) -
Cramer William A.,
Soriano Glenda M.,
Zhang Huamin,
Ponamarev Michael V.,
Smith Janet L.
Publication year - 1997
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.1399-3054.1997.tb00011.x
Subject(s) - cytochrome b6f complex , cytochrome , chemistry , astrobiology , biology , cytochrome b , biochemistry , gene , enzyme , mitochondrial dna
The Cyt b 6 f complex from plant chloroplasts, the green alga Chlamydomonas reinhardtii , and the thermophilic cyanobacterium, Mastigocladus laminosus , can be isolated in a highly active state, in which it is dimeric and contains one bound chlorophyll a molecule per monomeric unit. The latter feature is a distinguishing trait compared to the b 6 f complex of bacterial photosynthesis and the respiratory chain. In contrast to the trans‐membrane domains of the b 6 f complex, and of most other integral membrane proteins, which are characterized by an a ‐helical structure, the p ‐side peripheral domains, consisting of Cyt f and the Rieske protein, have a predominantly β‐strand secondary structure motif. One consequence of this motif is an extension of these polypeptides from the membrane surface. For example, the length of Cyt f is 75 Å. The heme Fe is 45 Å from the α‐carbon of Arg250 at the membrane bilayer interface and, even though Cyt f may be tilted relative to the membrane plane, the heme electron transfer reactions are carried out far from the membrane surface. The presence of an internal 5 water chain, which has the properties of a proton wire, with one water H‐bonded to the histidine‐25 heme ligand, also suggests that the pathway of long distance H + translocation traverses the extended p ‐side protein domain of the b 6 f complex. A mechanism of H + transfer in the chain that is coupled to the redox state of the heme, in which a proton is transferred into the chain to compensate the extra electron in the ferro‐heme, is proposed.