Abstract:
:Ubiquinol cytochrome c oxidoreductase (bc1 complex) serves as an important electron junction in many respiratory systems. It funnels electrons coming from NADH and ubiquinol to cytochrome c, but it is also capable of producing significant amounts of the free radical superoxide. In situ and in other experimental systems, the enzyme exists as a dimer. But until recently, it was believed to operate as a functional monomer. Here we show that a functional dimer model is capable of explaining both kinetic and superoxide production rate data. The model consists of six electronic states characterized by the number of electrons deposited on the complex. It is fully reversible and strictly adheres to the thermodynamics governing the reactions. A total of nine independent data sets were used to parameterize the model. To explain the data with a consistent set of parameters, it was necessary to incorporate intramonomer Coulombic effects between hemes bL and bH and intermonomer Coulombic effects between bL hemes. The fitted repulsion energies fall within the theoretical range of electrostatic calculations. In addition, model analysis demonstrates that the Q pool is mostly oxidized under normal physiological operation but can switch to a more reduced state when reverse electron transport conditions are in place.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Bazil JNdoi
10.1016/j.bpj.2017.08.018subject
Has Abstractpub_date
2017-10-03 00:00:00pages
1599-1612issue
7eissn
0006-3495issn
1542-0086pii
S0006-3495(17)30880-9journal_volume
113pub_type
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