ABSTRACT
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Mitochondria are the central organelles in cell bioenergetics. Most of the available oxygen is consumed in the electron transfer chain and is placed in the inner membrane of the two membranes that limit the differentiated mitochondrial
compartment. Electron transfer through mitochondrial complexes I-IV is joined to proton pumping across the inner membrane creating a proton electrochemical gradient between the intermembrane space and the matrix. This gradient (~0.15 V) is dissipated by the reentry of protons through ATPase channels that couple ATP synthesis to the electron transfer activity. From a classic perspective, it is accepted that the rate of this process is regulated by O2 and substrate availability as well as ADP/ATP ratio in response to cell demands. In the last few years, significant modulatory effects of nitric oxide (NO) resulted from its high-affinity binding to cytochrome oxidase, the final electron acceptor of electron transfer chain (1).
