Description

Additivity describes the princple of substrate control of mitochondrial respiration, where the additive effect of convergent CI&II electron flow is a consequence of electron flow converging at the Q-junction from respiratory Complexes I and II (CI&II e-input). Further additivity may be observed by convergent electron flow through glycerophosphate dehydrogenase and electron-transferring flavoprotein. Convergent electron flow corresponds to the operation of the TCA cycle and mitochondrial substrate supply in vivo. Physiological substrate combinations supporting convergent CI&II e-input are required for reconstitution of intracellular TCA cycle function. Convergent electron flow simultaneously through Complexes I and II (CI&II) into the Q-junction supports higher OXPHOS capacity and ETS capacity than separate electron flow through either CI or CII. The convergent CI&II effect may be completely or partially additive, suggesting that conventional bioenergetic protocols with mt-preparations have underestimated cellular OXPHOS capacities, due to the gating effect through a single branch. Complete additivity is defined as the condition when the sum of separatly measured respiratory capacities, CI + CII, is identical to the capacity measured in the state with combined substrates, CI&II. This condition of complete additivity, CI&II=CI+CII, would be obtained if electron channeling through supercomplex CI, CIII and CIV does not interact with the pool of redox intermediates in the pathway from CII to CIII and CIV, and if the capacity of the phosphorylation system (~P) does not limit OXPHOS capacity (). In most cases, however, additivity is incomplete, CI&II<CI+CII.

Abbreviation: A_α&β

Reference: Gnaiger 2014 MitoPathways, Gnaiger_2009_Int J Biochem Cell Biol

MitoPedia methods: Respirometry

MitoPedia topics: Substrate and metabolite

List of publications: CI and CII and CI&II

List of publications: CI and CII and CI&II and GpDH