Description
The mitochondrial electron transfer system (ETS) transfers electrons from externally supplied reduced fuel substrates to oxygen. Based on this experimentally oriented definition (see ETS capacity), the ETS consists of (1) the membrane-bound ETS with respiratory complexes located in the inner mt-membrane, (2) TCA cycle and other mt-matrix dehydrogenases generating NADH and succinate, and (3) the transport systems involved in metabolite exchange across the mt-membranes. Β» MiPNet article
Abbreviation: ETS
Reference: Gnaiger 2009 Int J Biochem Cell Biol, Gnaiger 2014 MitoPathways
MitoPedia concepts:
MiP concept
MitoPedia methods:
Respirometry
MitoPedia topics: Enzyme, EAGLE
Electron transfer system versus electron transport chain
Gnaiger E (2017) Electron transfer system versus electron transport chain. Mitochondr Physiol Network 2010-08-17, edited 2014-07-06, 2017-02-17. |
Abstract: Conventionally, the 'electron transport chain' has been considered as the sequence of membrane-bound respiratory complexes, mainly CI and CII feeding electrons into the Q-junction, and CIII and CIV linked by cytochrome c. Emphasis on the term electron transfer system clarifies (i) the convergent structure of the mitochondrial pathways, (ii) the upstream modules of electron transfer from externally supplied fuel substrates, transport into the matrix space, and matrix dehydrogenases, including the TCA cycle and the N-junction.
β’ O2k-Network Lab: AT Innsbruck Gnaiger E
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HRR: Theory
- The well established terms 'respiratory chain' or 'electron transfer chain' suggest erroneously that the convergent electron transfer system may be designed as a simple chain. But the term electron transport chain (or electron transfer chain, ETC) is a misnomer. Understanding mitochondrial respiratory control has suffered greatly from this inappropriate terminology, although textbooks using the term ETC (Lehninger 1970) make it sufficiently clear that electron transfer systems are not arranged as a chain: the βETCβ is in fact not a simple chain but an arrangement of electron transfer complexes in a non-linear, convergent electron transfer system. The classically introduced term electron transfer system (Hatefi et al 1962) is accurate and sufficient (IUB 1991).
- The established convention of defining the 'electron transport chain' as being comprised of four Complexes has conceptual weaknesses.
- (a) In fact, there are more than six Complexes of mitochondrial electron transfer (not including Complex V, which is not part of the ETS): CI to CIV, and additional respiratory complexes linked to pathways converging at the Q-junction (see Β»Pathway control state).
- (b) The term βchainβ suggests a linear sequence, whereas the functional structure of the electron transfer system can only be understood by recognizing the convergence of electron flow at the Q-junction, followed by a chain of Complexes III and IV, mediated by cytochrome c (Gnaiger 2014). Electrons flow to oxygen from either Complex I with a total of three coupling sites, or from Complex II and other flavoproteins, providing multiple entries into the Q-junction with two coupling sites downstream (Gnaiger 2014).
Electron transfer versus transport
- Electron transfer and electron transport are used synonymously. A general distinction, however, is helpful:
- (i) Transfer (inter- or intramolecular) of a reactant involves a chemical reaction.
- (ii) Transport (from one location to another) of an entity is a (vectorial) process in contrast to a chemical reaction (IUPAC Green Book).
Related MitoPedia pages
- Electron transfer system, ETS
- Pathway control states
- Coupling control state E