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 (1) mt-content in cells or tissues, (2) purification in preparations of isolated mitochondria, and (3) 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 2020 BEC MitoPathways, Gnaiger 2009 Int J Biochem Cell Biol, Doerrier 2018 Methods Mol Biol

Flux control efficiency: normalization of mitochondrial respiration

» More details: Flux control efficiency


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 E (2020) Mitochondrial pathways and respiratory control. An introduction to OXPHOS analysis. 5th ed. Bioenerg Commun 2020.2: 112 pp. doi:10.26124/bec:2020-0002.2020
Gnaiger Erich et al ― MitoEAGLE Task Group (2020) Mitochondrial physiology. Bioenerg Commun 2020.1. doi:10.26124/bec:2020-0001.v1.2020



Click to expand or collaps
Bioblast links: Coupling control - >>>>>>> - Click on [Expand] or [Collapse] - >>>>>>>

Mitochondrial and cellular respiratory rates in coupling-control states

OXPHOS-coupled energy cycles. Source: The Blue Book
» Baseline state
Respiratory rate Definition Icon
OXPHOS capacity P = -Rox P.jpg mt-preparations
ROUTINE respiration R = -Rox R.jpg living cells
ET capacity E = -Rox E.jpg » Level flow
» Noncoupled respiration - Uncoupler
LEAK respiration L = -Rox L.jpg » Static head
» LEAK state with ATP
» LEAK state with oligomycin
» LEAK state without adenylates
Residual oxygen consumption Rox L = -Rox ROX.jpg
  • Chance and Williams nomenclature: respiratory states
» State 1 —» State 2 —» State 3 —» State 4 —» State 5

Flux control ratios related to coupling in mt-preparations and living cells

» Flux control ratio
» Coupling-control ratio
» Coupling-control protocol
FCR Definition Icon
L/P coupling-control ratio L/P L/P coupling-control ratio » Respiratory acceptor control ratio, RCR = P/L
L/R coupling-control ratio L/R L/R coupling-control ratio
L/E coupling-control ratio L/E L/E coupling-control ratio » Uncoupling-control ratio, UCR = E/L
P/E control ratio P/E P/E control ratio
R/E control ratio R/E R/E control ratio
net P/E control ratio (P-L)/E net P/E control ratio
net R/E control ratio (R-L)/E net R/E control ratio

Net, excess, and reserve capacities of respiration

Respiratory net rate Definition Icon
P-L net OXPHOS capacity P-L P-L net OXPHOS  capacity
R-L net ROUTINE capacity R-L R-L net ROUTINE capacity
E-L net ET capacity E-L E-L net ET capacity
E-P excess capacity E-P E-P excess capacity
E-R reserve capacity E-R E-R reserve capacity

Flux control efficiencies related to coupling-control ratios

» Flux control efficiency jZ-Y
» Background state
» Reference state
» Metabolic control variable
Coupling-control efficiency Definition Icon Canonical term
P-L control efficiency jP-L = (P-L)/P = 1-L/P P-L control efficiency P-L OXPHOS-flux control efficiency
R-L control efficiency jR-L = (R-L)/R = 1-L/R R-L control efficiency R-L ROUTINE-flux control efficiency
E-L coupling efficiency jE-L = (E-L)/E = 1-L/E E-L coupling efficiency E-L ET-coupling efficiency » Biochemical coupling efficiency
E-P control efficiency jE-P = (E-P)/E = 1-P/E E-P control efficiency E-P ET-excess flux control efficiency
E-R control efficiency jE-R = (E-R)/E = 1-R/E E-R control efficiency E-R ET-reserve flux control efficiency


» Basal respiration
» Cell ergometry
» Dyscoupled respiration
» Dyscoupling
» Electron leak
» Electron-transfer-pathway state
» Hyphenation
» Oxidative phosphorylation
» Oxygen flow
» Oxygen flux
» Permeabilized cells
» Phosphorylation system
» Proton leak
» Proton slip
» Respiratory state
» Uncoupling


Click to expand or collaps
Bioblast links: Normalization - >>>>>>> - Click on [Expand] or [Collapse] - >>>>>>>

MitoPedia concepts: Respiratory control ratio, SUIT concept 

MitoPedia methods: Respirometry 

MitoPedia O2k and high-resolution respirometry: DatLab