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. 2020 Sep 27;11(2):52–61. doi: 10.4331/wjbc.v11.i2.52

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©The Author(s) 2020. Published by Baishideng Publishing Group Inc. All rights reserved.

This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial.

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Hypothesis on the variable binding of NDUFA4 to complex I or cytochrome c oxidase. A: Phosphorylation (P) of complex I and cytochrome c oxidase (CytOx) at low cytosolic calcium (< 1 micromolar) stabilizes binding of NDUFA4 to complex I and the function of the “allosteric ATP-inhibition” of dimeric CytOx (resting state); B: Stress-induced increase of cytosolic calcium (> 1 micromolar) dephosphorylates complex I and CytOx by a calcium-activated PP1, accompanied by monomerization of CytOx and switching off its allosteric ATP-inhibition. NDUFA4 is detached from complex I and binds to monomeric CytOx (excited state). At low cytosolic calcium, a cAMP-dependent protein kinase A phosphorylates complex I and CytOx. This changes the binding position of NDUFA4 from CytOx to complex I, accompanied by dimerization of CytOx and activation of its allosteric ATP-inhibition.