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Bioblasts - Richard Altmann and MiPArt by Odra Noel
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The Q-junction is a junction for convergent electron flow in the Electron transfer pathway (ET-pathway) from type N substrates and mt-matix dehydrogenases through Complex I (CI), from type F substrates and FA oxidation through electron-transferring flavoprotein complex (CETF), from succinate (S) through Complex II (CII), from glycerophosphate (Gp) through glycerophosphate dehydrogenase complex (CGpDH), from choline through choline dehydrogenase, from dihydro-orotate through dihydro-orotate dehydrogenase, and other enzyme complexes into the Q-cycle (ubiquinol/ubiquinone), and further downstream to Complex III (CIII) and Complex IV (CIV). The concept of the Q-junction, with the N-junction and F-junction upstream, provides the rationale for defining Electron-transfer-pathway states and categories of SUIT protocols.

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

MitoPedia concepts: MiP concept, SUIT concept 

MitoPedia methods: Respirometry 

MitoPedia topics: Enzyme 

Contributed by Gnaiger E 2010-08-15; edited 2016-02-12, 2016-03-28.

Convergent NS-linked electron flow at the Q-junction, exerting an additive effect on flux, versus electron gaiting for separation of single N- and S-input pathways (upper panel: Gnaiger 2009; lower panel: Hatefi 1962 J Biol Chem-XLII). Modified Fig. 1.5 in Gnaiger 2014 MitoPathways.

More details: »Respiratory complexes - more than five
» O2k-Publications: Q-junction effect


Related MitoPedia pages

  • Electron transfer pathway, ET-pathway
» Electron transfer pathway
» Q-junction
  • Electron-transfer-pathway state
» Electron-transfer-pathway state
  • Coupling control state E
E.jpg ET capacity
» Noncoupled respiration
» Is respiration uncoupled - noncoupled - dyscoupled?

SUITbrowser question: Q-junction

Several SUIT protocols can be used to answer questions on additivity, or convergence of electron flow to the Q-junction.
The SUITbrowser can be used to find the best SUIT protocols for different research questions, among those:
  • Q-junction (NS)
  • Q-junction (FNS)
  • Q-junction (FNSGp)