Description

The mitochondrial electron transfer system (ETS; synonymous with 'electron transport system') transfers electrons from externally supplied reduced substrates to oxygen. It consists of the membrane-bound ETS (mETS) with enzyme complexes located in the inner mt-membrane, mt-matrix dehydrogenases generating NADH, and the transport systems involved in metabolite exchange across the mt-membranes (see ETS capacity).

Abbreviation: ETS

Reference: Gnaiger 2009 Int J Biochem Cell Biol

MitoPedia methods: Respirometry

MitoPedia topics: "Respiratory state" is not in the list (Enzyme, Medium, Inhibitor, Substrate and metabolite, Uncoupler, Sample preparation, Permeabilization agent, EAGLE, MitoGlobal Organizations, MitoGlobal Centres, ...) of allowed values for the "MitoPedia topic" property. Respiratory state"Respiratory state" is not in the list (Enzyme, Medium, Inhibitor, Substrate and metabolite, Uncoupler, Sample preparation, Permeabilization agent, EAGLE, MitoGlobal Organizations, MitoGlobal Centres, ...) of allowed values for the "MitoPedia topic" property.

Gnaiger E (2013) Electron transfer system versus electron transport chain. Mitochondr Physiol Network 2013-08-18.

» Gnaiger 2012 MitoPathways

OROBOROS (2013) Mitochondr Physiol Network

Abstract: 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.

• O2k-Network Lab: AT Innsbruck Gnaiger E

Labels:

Coupling state: ETS"ETS" is not in the list (LEAK, ROUTINE, OXPHOS, ET) of allowed values for the "Coupling states" property.

HRR: Theory

Electron transfer system versus electron transport chain

Electron transfer system versus chain

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; Nicholls & Ferguson 2002) make it sufficiently clear that electron transfer systems are 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 system. The classically introduced term electron transfer system (Hatefi et al 1962 [1]) is accurate and sufficient [2].

The established convention of defining the 'electron transport chain' as being comprised of four Complexes has conceptual weaknesses.

(a) In fact, there are at least six Complexes of mitochondrial electron transfer: In addition to Complexes I and II, glycerophosphate dehydrogenase (GpDH) and electron transferring flavoprotein (ETF) are involved in the Q-junction with electron transfer to Complex III [2,3].

(b) The term „chain‟ 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.

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-cycle with two coupling sites downstream [2].

Electron transfer versus transport

Electron transfer and electron transport are used synonymously. A general distinction, however, may be helpful:

(i) Transfer (inter- or intramolecular) of a reactant involves a chemical reaction.

(ii) Transport (from one place to another) of an entity is a (vectorial) process in contrast to a chemical reaction [4].

References

Biochemical coupling efficiency