Electron input though Complexes CI plus CII simultaneously into the Q-junction corresponds to TCA cycle function in vivo, with convergent electron flow through the ETS. In mt-preparations, CI+II e-input requires addition not only of CI substrate (pyruvate+malate or glutamate+malate), but of succinate simultaneously, since metabolite depletion in the absence of succinate prevents a significant activity of CII.
References
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