An extended dynamic model of oxidative phosphorylation.

The presented model based on an earlier one (Korzeniewski, B. and Froncisz, W. (1989) Studia Biophys. 132, 173-187) simulates concentration changes in time of chemical compounds and thermodynamic forces during respiration of cell suspension in a closed chamber. A set of differential equations solved numerically describes the utilization of oxygen up to anaerobiosis and the behaviour of the system after a sudden pulse of oxygen. Flux control coefficients for most important reactions (enzymes) of oxidative phosphorylation were calculated. A good qualitative and (when a direct comparison is possible) quantitative agreement with experimental results can be observed. The following conclusions can be drawn from the simulation: (1) Wilson's steady state model is not in contradiction with sharing of the control over the respiration between some steps and displacement of the ATP/ADP carrier from equilibrium. (2) The overshoot characteristics of the delta microH+ time-course after reoxygenation can be explained without using the lag-phase kinetics of ATP-synthetase. (3) A 'hot region' (sharp changes of many parameters) can be distinguished when the oxygen concentration approaches zero; only cytochrome oxidase is clearly sensitive on oxygen concentration in all its range. (4) Control over oxidative phosphorylation is shared mainly between inputs of the system (ATP utilization and substrate dehydrogenation) and the proton leak.