Flux control ratio

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Flux control ratio


Flux control ratios (FCR), are ratios of oxygen flux in different respiratory control states, normalized for maximum flux in a common reference state, to obtain theoretical lower and upper limits of 0.0 and 1.0 (0% and 100%).

For a given protocol or set of respiratory protocols, flux control ratios provide a fingerprint of coupling and substrate control independent of (i) mt-content in cells or tissues, (ii) purification in preparations of isolated mitochondria, and (iii) assay conditions for determination of tissue mass or mt-markers external to a respiratory protocol (CS, protein, stereology, etc.). FCR obtained from a single respirometric incubation with sequential titrations (sequential protocol; SUIT protocol) provide an internal normalization, expressing respiratory control independent of mitochondrial content and thus independent of a marker for mitochondrial amount. FCR obtained from separate (parallel) protocols depend on equal distribution of subsamples obtained from a homogenous mt-preparation or determination of a common mitochondrial marker.

Abbreviation: FCR

Reference: Gnaiger 2014 MitoPathways, Gnaiger 2009 Int J Biochem Cell Biol, Doerrier 2018 Methods Mol Biol

Flux control factor: normalization of mitochondrial respiration

» More details: Flux control factor


Unknown sample concentration and normalization per unit sample [x]

  • In the DatLab 7.4 Excel template for oxygen flux analysis (O2 analysis template DL7.4):
If the sample concentration is not yet known, the box ‘Known sample concentration’ can be unchecked, and the concentration will be considered by default as 1, with units [x·mL-1]. In this way, flux can be normalized and FCRs can be obtained even if the sample concentration is unknown.
» Read also: Extensive quantity; BEC 2020.1
» More details: MiPNet24.06 Oxygen flux analysis - DatLab 7.4

FCR in DatLab plot

  • The entire plot of oxygen flux can be converted to a FCR. Click on 'Flux/Slope' in the DatLab pull-down menu. Select chamber A or B 'O2 slope'. Select 'Flux control ratio, FCR' and select the mark that corresponds to the reference state. Change the scale under 'Graph/Scaling' (or press F6).
» More details: Flux/Slope in DatLab


Bioblast linkReferenceYear
Doerrier C, Garcia-Souza LF, Krumschnabel G, Wohlfarter Y, Mészáros AT, Gnaiger E (2018) High-Resolution FluoRespirometry and OXPHOS protocols for human cells, permeabilized fibers from small biopsies of muscle, and isolated mitochondria. Methods Mol Biol 1782:31-70.2018
Gnaiger E (2009) Capacity of oxidative phosphorylation in human skeletal muscle. New perspectives of mitochondrial physiology. Int J Biochem Cell Biol 41:1837-45.2009
Gnaiger Erich et al ― MitoEAGLE Task Group (2020) Mitochondrial physiology. Bioenerg Commun 2020.1. doi:10.26124/bec:2020-0001.v1.2020
Gnaiger E (2014) Mitochondrial pathways and respiratory control. An introduction to OXPHOS analysis. 4th ed. Mitochondr Physiol Network 19.12. Oroboros MiPNet Publications, Innsbruck:80 pp.


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MitoPedia concepts: Respiratory control ratio, SUIT concept 

MitoPedia methods: Respirometry 

MitoPedia O2k and high-resolution respirometry: DatLab