Regulation of cytochrome c oxidase contributes to health and optimal life.

Abstract

The generation of cellular energy in the form of ATP occurs mainly in mitochondria by oxidative phosphorylation. Cytochrome c oxidase (CytOx), the oxygen accepting and rate-limiting step of the respiratory chain, regulates the supply of variable ATP demands in cells by "allosteric ATP-inhibition of CytOx." This mechanism is based on inhibition of oxygen uptake of CytOx at high ATP/ADP ratios and low ferrocytochrome c concentrations in the mitochondrial matrix via cooperative interaction of the two substrate binding sites in dimeric CytOx. The mechanism keeps mitochondrial membrane potential ΔΨ_m and reactive oxygen species (ROS) formation at low healthy values. Stress signals increase cytosolic calcium leading to Ca²⁺-dependent dephosphorylation of CytOx subunit I at the cytosolic side accompanied by switching off the allosteric ATP-inhibition and monomerization of CytOx. This is followed by increase of ΔΨ_m and formation of ROS. A hypothesis is presented suggesting a dynamic change of binding of NDUFA4, originally identified as a subunit of complex I, between monomeric CytOx (active state with high ΔΨ_m, high ROS and low efficiency) and complex I (resting state with low ΔΨ_m, low ROS and high efficiency).