Journal
BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS
Volume 1757, Issue 5-6, Pages 339-345Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.bbabio.2006.04.020
Keywords
carbon fixation; cytochrome b(6)f, bc(1) complexes; cyclic electron transport; heme c(n); Q cycle
Categories
Funding
- NIGMS NIH HHS [GM-38323] Funding Source: Medline
Ask authors/readers for more resources
At least two features of the crystal structures of the cytochrome b(6)f complex from the thermophilic cyanobacterium, Mastigocladus laminosus and a green alga, Chlamydomonas reinhardtii, have implications for the pathways and mechanism of charge (electron/proton) transfer in the complex: (i) The narrow 11 x 12 angstrom portal between the p-side of the quinone exchange cavity and p-side plastoquinone/quinol binding niche, through which all Q/QH(2) must pass, is smaller in the b(6)f than in the bc(1) complex because of its partial occlusion by the phytyl chain of the one bound chlorophyll a molecule in the b(6)f complex. Thus, the pathway for trans-membrane passage of the lipophilic quinone is even more labyrinthine in the b(6)f than in the bc(1) complex. (ii) A unique covalently bound heme, heme c(n), in close proximity to the n-side b heme, is present in the b(6)f complex. The b(6)f structure implies that a Q cycle mechanism must be modified to include heme c(n) as an intermediate between heme b(n) and plastoquinone bound at a different site than in the bc(1) complex. In addition, it is likely that the heme b(n)-c(n) couple participates in photosytem I-linked cyclic electron transport that requires ferredoxin and the ferredoxin: NADP(+) reductase. This pathway through the n-side of the b(6)f complex could overlap with the n-side of the Q cycle pathway. Thus, either regulation is required at the level of the redox state of the hemes that would allow them to be shared by the two pathways, and/or the two different pathways are segregated in the membrane. (c) 2006 Elsevier B.V. All rights reserved.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available