... areclosely interlinked in the function of the enzyme complex.Studies in yeast have shown that both oxygen and heme actas physiological modulators and regulate the expression of the enzyme complex ... (CytOX) is the terminal oxidase of the mitochondrial electron transport chain [1–5], whichcatalyzes the reduction of the dioxygen (O2) to water and harnesses the free energy of the reaction ... [4,5]. The remaining 10 subunits of the mammalian enzyme, namely, IV, Vb, VIa, VIb, VIc, VIIa,VIIb and VIII are encoded by the nuclear genome,synthesized in the cytosol and imported into mitochondria[1–3]....