ISSN:
1573-6881
Keywords:
quinone
;
cytochrome b 6
;
cytochrome f
;
cytochrome complexes, membrane-bound
;
electron transfer
;
intraprotein
;
iron–sulfur protein
;
membranes, energy transduction
;
proton translocation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Physics
Notes:
Abstract Structural alignment of the integral cytochrome b 6-SU IV subunits with the solved structure of themitochondrial bc 1 complex shows a pronounced asymmetry. There is a much higher homology onthe p-side of the membrane, suggesting a similarity in the mechanisms of intramembrane andinterfacial electron and proton transfer on the p-side, but not necessarily on the n-side. Structuraldifferences between the bc 1 and b 6 f complexes appear to be larger the farther the domain or subunitis removed from the membrane core, with extreme differences between cytochromes c 1 and f. Aspecial role for the dimer may involve electron sharing between the two hemes b p, which is indicatedas a probable event by calculations of relative rate constants for intramonomer heme b p → hemeb n, or intermonomer heme b p → heme b p electron transfer. The long-standing observation offlash-induced oxidation of only ∼0.5 of the chemical content of cyt f may be partly a consequence ofthe statistical population of ISP bound to cyt f on the dimer. It is proposed that the p-side domainof cyt f is positioned with its long axis parallel to the membrane surface in order to: (i) allow itslarge and small domains to carry out the functions of cyt c 1 and suVIII, respectively, of the bc 1complex, and (ii) provide maximum dielectric continuity with the membrane. (iii) This positionwould also allow the internal water chain (“proton wire”) of cyt f to serve as the p-side exit portfor an intramembrane H+ transfer chain that would deprotonate the semiquinol located in themyxothiazol/MOA-stilbene pocket near heme b p. A hypothesis is presented for the identity of theamino acid residues in this chain.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1005463527752
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