Kinetic evidence against partitioning of the ubiquinone pool and the catalytic relevance of respiratory-chain supercomplexes.

TitleKinetic evidence against partitioning of the ubiquinone pool and the catalytic relevance of respiratory-chain supercomplexes.
Publication TypeJournal Article
Year of Publication2014
AuthorsBlaza, JN, Serreli, R, J Y Jones, A, Mohammed, K, Hirst, J
JournalProc Natl Acad Sci U S A
Volume111
Issue44
Pagination15735-40
Date Published2014 Nov 4
ISSN1091-6490
KeywordsAnimals, Cattle, Electron Transport, Electron Transport Complex I, Kinetics, Mitochondria, Heart, Models, Chemical, NAD, Oxidation-Reduction, Succinic Acid, Ubiquinone
Abstract

In mitochondria, four respiratory-chain complexes drive oxidative phosphorylation by sustaining a proton-motive force across the inner membrane that is used to synthesize ATP. The question of how the densely packed proteins of the inner membrane are organized to optimize structure and function has returned to prominence with the characterization of respiratory-chain supercomplexes. Supercomplexes are increasingly accepted structural entities, but their functional and catalytic advantages are disputed. Notably, substrate "channeling" between the enzymes in supercomplexes has been proposed to confer a kinetic advantage, relative to the rate provided by a freely accessible, common substrate pool. Here, we focus on the mitochondrial ubiquinone/ubiquinol pool. We formulate and test three conceptually simple predictions of the behavior of the mammalian respiratory chain that depend on whether channeling in supercomplexes is kinetically important, and on whether the ubiquinone pool is partitioned between pathways. Our spectroscopic and kinetic experiments demonstrate how the metabolic pathways for NADH and succinate oxidation communicate and catalyze via a single, universally accessible ubiquinone/ubiquinol pool that is not partitioned or channeled. We reevaluate the major piece of contrary evidence from flux control analysis and find that the conclusion of substrate channeling arises from the particular behavior of a single inhibitor; we explain why different inhibitors behave differently and show that a robust flux control analysis provides no evidence for channeling. Finally, we discuss how the formation of respiratory-chain supercomplexes may confer alternative advantages on energy-converting membranes.

DOI10.1073/pnas.1413855111
Alternate JournalProc. Natl. Acad. Sci. U.S.A.
Citation Key10.1073/pnas.1413855111
PubMed ID25331896
PubMed Central IDPMC4226120
Grant ListMC_U105663141 / / Medical Research Council / United Kingdom
U105663141 / / Medical Research Council / United Kingdom