# ðŸ“’ Bazil 2013

Contents

Catalytic coupling of oxidative phosphorylation, ATP demand, and reactive oxygen species generation

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## Introduction

The biochemical equation of Complex III for the net reaction is shown as

Previous models are either too simple or too complex

The model developed here maintains the features presented above in a tenable, well-constrained representation of the bc1 complex

## Methods

### Model structure

- This model includes the redox biochemistry that occurs at the Qo-site and Qi-site of the complex and couples cyt c reduction with the first electron transfer from ubiquinol
- This first electron transfer at the Qo-site is the one of the primary, rate-limiting steps in the catalytic cycle
- we assume that up to two mobile electrons can exist at both the Qo-site and Qi-site
- 6 states
- The fractional substate occupancies and the state transitions are governed by the thermodynamic driving force of the redox biochemistry defined by the midpoint potentials some of them being pH-dependent
- Binding polynomials for Qo, Qi site, and ISP FeS
- Under the right circumstances when cyt bL is reduced, there is a small but significant level of SQ at the Qo-site
- State transitions are governed by two primary Gibbâ€™s free energies of reaction.
- The net turnover flux through the enzyme:
- Superoxide production rate:
- analytic expressions for the states at steady state
- The analytical solution for each state contains âˆ¼1000 terms, so they are not explicitly presented here (using KA method ?)

## Results and Discussion

- Table1: fixed parameter values obtained from the literature and used to simulate the model
- midpoint potentials, stability constants, pKa values, and other parameters

- Table2: fitted parameter values and sesitivity

- The cyt c binding constants were assumed to be similar to the fitted constants for horse heart cyt c, based on its apparent universal nature as a substrate for bc1 complexes from other species

## Reference

Bazil JN, Vinnakota KC, Wu F, Beard DA. Analysis of the kinetics and bistability of ubiquinol:cytochrome c oxidoreductase. Biophys J. 2013;105(2):343-55. PMC3714890 ↩︎