Description
Residual oxygen consumption, ROX, is the respiration due to oxidative side reactions remaining after application of ETS inhibitors to mitochondrial preparations or cells, or in mt-preparations incubated without substrates (in the presence of ADP: State 2). Mitochondrial respiration is frequently corrected for ROX, then distinguishing ROX-corrected ROUTINE, LEAK, OXPHOS or ETS (R, L, P and E) from the corresponding apparent fluxes that have not been corrected for ROX (RΒ΄, LΒ΄, PΒ΄ and EΒ΄). When expressing ROX as a fraction of total respiration (flux control ratio), apparent flux not corrected for ROX should be taken as the reference. ROX may be related to, but is of course different from ROS production. Β» MiPNet article
Abbreviation: ROX
Reference: Gnaiger 2014 MitoPathways, Gnaiger 2009 Int J Biochem Cell Biol
MitoPedia concepts:
Respiratory state
MitoPedia methods:
Respirometry
ROX or non-mitochondrial respiration and potential artefacts
Gnaiger E (2016) ROX or non-mitochondrial respiration and potential artefacts. Mitochondr Physiol Network 2016-01-28. |
Abstract: Residual oxygen consumption (ROX) is sometimes referred to as 'non-mitochondrial respiration'. This may be correct to a large extent, but is not entirely accurate. In a preparation of purified isolated mitochondria, a small but significant ROX is observed, even after correction for instrumental background oxygen flux. In this case, ROX is 'mitochondrial non-ETS' rather than βnon-mitochondrialβ respiration. In permeabilized and intact cells, ROX may be higher than in isolated mitochondria, and this increased part then would be the best measurement of non-mitochondrial respiration. Keilin (1926) introduced and accurately defined the term residual respiration.
β’ 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
Keilin 1929: Residual respiration
- 'KCN, H2S and CO combine with some of the components of oxidase forming an inactive compound, with the result that cytochrome, or at least its components aβ and cβ, as well as paraphenylenediamine added to the cells, are not oxidised. The respiratory process can be still carried out through the medium of some autoxidisable carriers such as haemochromogens, haematins, the component bβ of cytochrome, or some as yet unknown autoxidisable substances. This residual respiration, according to the nature of the cell, may represent a larger or smaller fraction of the total respiration of the cell.'
- Keilin D (1929) Cytochrome and respiratory enzymes. Proc R Soc London Ser B 104:206-52.
Experimental tests on ROX
Is the preparation fully permeabilized?
- ROX may be estimated in mitochondrial preparations in SUIT protocols which start at a respiratory state without added CHO substrates and without inhibitors, such that continuation of the SUIT protocol is possible for OXPHOS analysis. Some critical questions arise for evaluation, if this respiratory 'ROX state' represents a valid condition for estimation of ROX, and for comparison with ROX measured at the end of a SUIT protocol after titration of substrates and inhibitors of key elements of the electron transfer system (e.g. Rot, Mna and Ama as inhibitors of CI, CII and CIII). For evaluation of such an initial estimate of ROX, the following considerations are suggested.
- A preparation of permeabilized tissue or cells, Ptic, may contain a fraction of intact, non-permeabilized cells. Non-permeabilized cells have ROUTINE respiration that
- is higher than ROX;
- is not stimulated by addition of ADP;
- is not diminished over prolonged periods of time due to the presence of cellular endogenous substrates;
- can be stimulated by uncoupler titration;
- can be inhibited by Rot (CI) and Ama (CII), etc.
- Respiration of permeabilized tissue or cells incubated in a medium with significant concentrations of mitochondrial substrates
- is higher than ROX;
- is stimulated by addition of ADP (compare 1.2);
- is not diminished over prolonged periods of time due to the presence of exogenous substrates in the medium;
- can be stimulated by uncoupler titration,
- can be inhibited by Rot (CI) and Ama (CII), etc.
- In contrast, the acutal level of ROX of fully permeabilized cells responds to such tests as
- ROX is obtained after gradual depletion of mitochondrial internal substrates (gradual decline of oxygen consumption);
- ADP or uncoupler titrations accelerate this decline;
- Rot and Ama do not inhibit ROX;
- uncoupler titration does not stimulate ROX.
- A preparation of permeabilized tissue or cells, Ptic, may contain a fraction of intact, non-permeabilized cells. Non-permeabilized cells have ROUTINE respiration that
Related terms in Bioblast
- OXPHOS, P
- ROUTINE, R
- ETS, E
- LEAK, L
- ROX, R