- high-resolution terminology - matching measurements at high-resolution
Flux control ratio
Description
Flux control ratios express respiratory control independent of mitochondrial content and cell size. FCR are 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%).
1. ROX/Eโ: The ROX/Eโ ratio is low (0.01 to 0.07; Tab. 1), but ROX contributes to a significant extent to LEAK respiration, with corresponding ROX/Lโ ratios ranging from 0.1 to 0.3, and up to 0.5 in growth-arrested fibroblasts (Tab. 1). 2. L/E: The LEAK control ratio is the ratio of LEAK respiration and ETS capacity. L/E ranges from 0.09 to 0.14 in various cells (Tab. 1; the inverse, 11 to 7, is the respiratory control ratio, RCR; ref. 1,11). Dyscoupling increases the L/E ratio, e.g. to 0.21 in senescent fibroblasts (Tab. 1). Alternatively, the L/E ratio may increase without intrinsic uncoupling or dyscoupling, if ETS capacity is diminished. It is, therefore, important to evaluate potential defects of ETS capacity per mt-marker, e.g. ETS per citrate synthase activity (5,8,11). 3. R/E: The ROUTINE control ratio is the ratio of (coupled) ROUTINE respiration and (noncoupled) ETS capacity. R/E ranges from 0.2 to 0.4 (Tab. 1; the inverse of 5 to 2.5 is the uncoupling control ratio, UCR; ref. 3-8). The R/E ratio is an expression of how close ROUTINE respiration operates to ETS capacity. Reported R/E ratios๏ฟฝ0.5 (15) could not be reproduced by HRR in a wide range of human cell types and incubation conditions (Tab. 1). The discrepancies cannot be fully explained by high glucose concentrations in culture and respiration media, since glucose exerts an effect not only on R but also on E (13). R/E ratios increase due to (i) high ATP demand and ADP-stimulated ROUTINE respiration, (ii) dyscoupling (senescent fibroblasts; Tab. 1), and (iii) limitation of respiratory capacity by defects of substrate oxidation and complexes of the ETS. 4. (R-L)/E: The netROUTINE control ratio, (R-L)/E, expresses phosphorylation-related respiration (corrected for LEAK respiration) as a fraction of ETS capacity. 0.1 to 0.3 of ETS capacity is used for oxidative phosphorylation under ROUTINE conditions (Tab. 1). (R-L)/E remains constant, if dyscoupling is fully compensated by an increase of ROUTINE respiration and a constant rate of oxidative phosphorylation is maintained (fibroblasts in Tab. 1). Upon stimulation of OXPHOS by an increased ATP demand, or if the respiratory capacity declines without effect on the rate of OXPHOS, however, (R-L)/E increases, which indicates that a higher proportion of the maximum capacity is activated to drive ATP synthesis. (R-L)/E declines to zero in either fully uncoupled cells (R=L=E) or in cells under metabolic arrest (R=L<E). 5. If the PC protocol is extended by measurement of cytochrome c oxidase, then the ratio of CIV activity and non-coupled respiration is an index of the apparent excess capacity of this enzyme step in the ETS. Autooxidation of ascorbate and TMPD (Tab. 2) is extremely high in culture media, hence a mitochondrial respiration medium is used (5).
Abbreviation: FCR
Reference: MiPNet12.15; Pesta_2010_Protocol
Labels:
Regulation: Respiration; OXPHOS; ETS Capacity"Respiration; OXPHOS; ETS Capacity" is not in the list (Aerobic glycolysis, ADP, ATP, ATP production, AMP, Calcium, Coupling efficiency;uncoupling, Cyt c, Flux control, Inhibitor, ...) of allowed values for the "Respiration and regulation" property., Flux Control; Additivity; Threshold; Excess Capacity"Flux Control; Additivity; Threshold; Excess Capacity" is not in the list (Aerobic glycolysis, ADP, ATP, ATP production, AMP, Calcium, Coupling efficiency;uncoupling, Cyt c, Flux control, Inhibitor, ...) of allowed values for the "Respiration and regulation" property.
