Recent experimental results indicate that oxidative phosphorylation in mitochondria is not only regulated by “respiratory control”, i.e., inhibition of respiration at low ATP utilization via the electrochemical proton gradient across the inner mitochondrial membrane, but in addition by reversible phosphorylation of respiratory chain complexes and of ATP synthase. Thus the formation of ATP and the generation of heat by mitochondria is also controlled by second messenger-mediated signal transduction mechanisms. The second messengers include cAMP, calcium, and ROS leading to activation of mitochondrial protein kinases and phosphatases. Some protein kinases (e.g., PKB = Akt, PKC) have been demonstrated to be translocated into mitochondria after activation (phosphorylation) outside of mitochondria. Subunit phosphorylation has been described for complexes I (NADH dehydrogenase), II (succinate dehydrogenase), III (cytochrome c reductase), IV (cytochrome c oxidase) and V (ATP synthase). Of particular interest is the phosphorylation of complex IV leading to an allosteric ATP-inhibition of cytochrome c oxidase, representing a second mechanism of respiratory control.
Keywords: Mitochondria, oxidative phosphorylation, protein phosphorylation, NADH dehydrogenase, cytochrome c oxidase, ATP synthase, mitochondrial membrane potential, ROS formation, signal transduction