Theoretical studies on the control of the oxidative phosphorylation system.

The dynamic model developed in our previous publications [1,2] was used to calculate the flux control coefficients of oxidation, phosphorylation and proton leak fluxes for isolated mitochondria and for three modes of work of intact cells (hepatocytes). The results obtained were compared with experimental data, especially those measured in the frame of the 'top-down approach' of the metabolic control theory. A good agreement for mitochondria and for intact cells was found. The control of the oxygen consumption flux is shared between the ATP utilization (main controlling factor), substrate dehydrogenation, proton leak and, in some conditions, the ATP/ADP carrier. The phosphorylation subsystem seemed to be controlled mainly by itself, while the proton leak was influenced by all three subsystems. It was also shown that the large relative change in the enzyme activity during inhibitor titration of mitochondria or cells could lead to the overestimation of some flux control coefficient values in experimental measurements. An influence of some hormones (glucagon, vasopressin, adrenaline and others) on the mitochondrial respiration was also simulated. Our results suggest that these hormones stimulate the substrate dehydrogenation as well as the phosphorylation system (ATP usage and, possibly, the ATP/ADP carrier).