Chemistry Reference
In-Depth Information
(a)
(b)
(c)
FIGURE 13.15
The yeast ubiquinol-cytochrome c oxidoreductase, QCR, or cytochrome bc
1
complex. (a) the homodimeric complex of the
catalytic subunits cytochrome b, orange, Rieske protein, green, and cytochrome c1, yellow. The second functional unit is coloured in grey. (b)
Schematic representation of one functional subunit. The Rieske protein is anchored with its transmembrane helix in one monomer, while the
extrinsic domain forms a functional unit with the catalytic subunits of the other monomer. Qo sites are depicted as diamonds, Qi sites as circles.
(c) Orientation of cofactors, substrate, and inhibitor molecules in yeast QCR. Monomers A and B are colour coded in red and blue, respectively.
The extrinsic domain of the protein is mobile and the Fe
2
e
S
2
cluster can be found in different orientations with the maximal positions either
close to haem bL (b-position) or close to haem c1 (c-position). The latter orientation is found in a bovine QCR structure (X, PDB entry: 1BE3)
and the Fe
2
e
S
2
cluster of the superimposed model is coloured in green. In yeast, stigmatellin specifically binds to the Qo site stabilising the
b-position and inhibiting enzyme activity. Electron transfer and proton uptake are indicated with straight arrows. The curved arrow represents
the movement of the Fe
2
e
S
2
cluster, which most likely precedes oxidation of the cluster by cytochrome c1. The spatial arrangement of the
cofactors allows fast electron transfer.
(From
Hunte, 2001
.
Copyright 2001 with permission from Elsevier.)
