ISSN:
1573-6881
Keywords:
Ubiquinone
;
bc 1 complex
;
cytochromec reductase
;
cytochromeb
;
iron-sulfur protein
;
electrogenic e− transport
;
redox-linkedpK change
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Physics
Notes:
Abstract The arrangement and function of the redox centers of the mammalianbc 1 complex is described on the basis of structural data derived from amino acid sequence studies and secondary structure predictions and on the basis of functional studies (i.e., EPR data, inhibitor studies, and kinetic experiments). Two ubiquinone reaction centers do exist—a QH2 oxidation center situated at the outer, cytosolic surface of the cristae membrane (Q0 center), and a Q reduction center (Q i center) situated more to the inner surface of the cristae membrane. The Q0 center is formed by theb-566 domain of cytochromeb, the FeS protein, and maybe an additional small subunit, whereas the Q i center is formed by theb-562 domain of cytochromeb and presumably the 13.4kDa protein (“QP-C”). The “Q binding proteins” are proposed to be protein subunits of the Q reaction centers of various multiprotein complexes. The path of electron flow branches at the Q0 center, half of the electrons flowing via the high-potential cytochrome chain to oxygen and half of the electrons cycling back into the Q pool via the cytochromeb path connecting the two Q reaction centers. During oxidation of QH2, 2H+ are released to the cytosolic space and during reduction of Q, 2H+ are taken up from the matrix side, resulting in a net transport across the membrane of 2H+ per e− flown from QH2 to cytochromec, the H+ being transported across the membrane as H (H+ + e−) by the mobile carrier Q. The authors correct their earlier view of cytochromeb functioning as a H+ pump, proposing that the redox-linkedpK changes of the acidic groups of cytochromeb are involved in the protonation/deprotonation processes taking place during the reduction and oxidation of Q. The reviewers stress that cytochromeb is in equilibrium with the Q pool via the Q i center, but not via the Q0 center. Their view of the mechanisms taking place at the reductase is a Q cycle linked to a Q-pool where cytochromeb is acting as an electron pump.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00743462
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