Metabolic control over the oxygen consumption flux in intact skeletal muscle: in silico studies.

It has been postulated previously that a direct activation of all oxidative phosphorylation complexes in parallel with the activation of ATP usage and substrate dehydrogenation (the so-called each-step activation) is the main mechanism responsible for adjusting the rate of ATP production by mitochondria to the current energy demand during rest-to-work transition in intact skeletal muscle in vivo. The present in silico study, using a computer model of oxidative phosphorylation developed previously, analyzes the impact of the each-step-activation mechanism on the distribution of control (defined within Metabolic Control Analysis) over the oxygen consumption flux among the components of the bioenergetic system in intact oxidative skeletal muscle at different energy demands. It is demonstrated that in the absence of each-step activation, the oxidative phosphorylation complexes take over from ATP usage most of the control over the respiration rate and oxidative ATP production at higher (but still physiological) energy demands. This leads to a saturation of oxidative phosphorylation, impossibility of a further acceleration of oxidative ATP synthesis, and dramatic drop in the phosphorylation potential. On the other hand, the each-step-activation mechanism allows maintenance of a high degree of the control exerted by ATP usage over the ATP turnover and oxygen consumption flux even at high energy demands and thus enables a potentially very large increase in ATP turnover. It is also shown that low oxygen concentration shifts the metabolic control from ATP usage to cytochrome oxidase and thus limits the oxidative ATP production.