Electron transfer-pathway

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Electron transfer-pathway

Description

In the mitochondrial electron transfer-pathway (ET-pathway) electrons are transfered from externally supplied reduced fuel substrates to oxygen. Based on this experimentally oriented definition (see ET-capacity), the ET-pathway consists of (1) the membrane-bound ET-pathway with respiratory complexes located in the inner mt-membrane, (2) TCA cycle and other mt-matrix dehydrogenases generating NADH and succinate, and (3) the carriers involved in metabolite transport across the mt-membranes. » MiPNet article

Abbreviation: ET-pathway

Reference: Gnaiger 2009 Int J Biochem Cell Biol, Gnaiger 2014 MitoPathways


MitoPedia concepts: MiP concept 


MitoPedia methods: Respirometry 



MitoPedia topics: Enzyme, EAGLE 

Electron transfer pathway versus electron transport chain

Publications in the MiPMap
Gnaiger E (2017) Electron transfer pathway versus electron transport chain. Mitochondr Physiol Network 2010-08-17, edited 2014-07-06, 2017-02-17, 2017-10-10.

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Oroboros (2017) MiPNet

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 pathway (or Electron transfer-pathway, Gnaiger 2014 MitoPathways) 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.


O2k-Network Lab: AT Innsbruck Gnaiger E


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HRR: Theory 


Q-junction
The well established terms 'respiratory chain' or 'electron transfer chain' suggest erroneously that the convergent electron transfer pathway 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 is not arranged as a chain: the „ETC‟ is in fact not a simple chain but an arrangement of electron transfer complexes in a non-linear, convergent electron transfer pathway. The classically introduced term Electron transfer-pathway (Hatefi et al 1962) is more accurate. Since the enzyme-catalyzed steps form a metabolic pathway, the term electron transfer pathway 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 ET-pathway): CI to CIV, and additional respiratory complexes linked to pathways converging at the Q-junction (see »Electron transfer-pathway state).
(b) The term „chain‟ suggests a linear sequence, whereas the functional structure of the electron transfer pathway 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 pathway, ET pathway
» Electron transfer-pathway
» Q-junction
  • ET-pathway states
» ET-pathway state
  • Coupling control state E
E.jpg ET-capacity
» Noncoupled respiration
» Is respiration uncoupled - noncoupled - dyscoupled?