Gnaiger 2014 Abstract MiP2014
Cell ergometry: OXPHOS and ETS coupling efficiency. |
Link:
Mitochondr Physiol Network 19.13 - MiP2014
Gnaiger E (2014)
Event: MiP2014
Biochemical cell ergometry aims at measurement of JO2,max (compare VO2,max in exercise ergometry of humans and animals) of cell respiration linked to phosphorylation of ADP to ATP. The corresponding OXPHOS capacity is based on saturating concentrations of ADP, [ADP]*, and inorganic phosphate, [Pi]*, available to the mitochondria. This is metabolically opposite to uncoupling respiration, which yields ETS capacity. The OXPHOS state can be established experimentally by selective permeabilization of cell membranes with maintenance of intact mitochondria, titrations of ADP and Pi to evaluate kinetically saturating conditions, and establishing fuel substrate combinations which reconstitute physiological TCA cycle function.
Labels: MiParea: Respiration
Coupling state: OXPHOS
HRR: Oxygraph-2k Event: A4, Oral MiP2014
Affiliation
1-Daniel Swarovski Research Lab, Mitochondrial Physiol, Dep Visceral, Transplant Thoracic Surgery, Medical Univ Innsbruck; 2-OROBOROS INSTRUMENTS, Innsbruck, Austria. - [email protected]
Abstract
Analogous to ergometric measurement of VO2max or VO2peak on a cycle or treadmill, cell ergometry is based on OXPHOS analysis to determine OXPHOS capacity, JO2P=P [pmol O2Β·s-1Β·mg-1], at the cellular and mitochondrial level. VO2peak and JO2P provide reference values for a subjectβs or a cellβs aerobic or mitochondrial competence. Aerobic catabolic flux (1 ml O2Β·min-1Β·kg-1 = 0.744 Β΅molΒ·s-1Β·kg-1) is multiplied by the corresponding Gibbs force (ΞkGO2=βG/βkΞΎO2; typically -470 kJ/mol or -0.48 J/Β΅mol O2) to obtain the mass-specific aerobic input power [WΒ·kg-1]. The corresponding mechanical output power, Ppeak [WΒ·kg-1], in cycle ergometry results in ergodynamic efficiencies [1] of about 0.25,
Ξ΅peak = Ppeak/-(JO2peakΒ·ΞkGO2) = (Ppeak/JO2peak) / -ΞkGO2 (1)
In OXPHOS analysis the output power is mitochondrial ATP production, J~P=~P, times the Gibbs force of phosphorylation (ΞpG~P=βG/βpΞΎ~P), which is typically 48 to 62 kJ/mol ~P [1]. Ergodynamic efficiency is a power ratio, partitioned into a flux ratio (the famous ~P/O2 ratio; ATP yield per oxygen consumed, Y~P/O2 = J~P/JO2P = ~P/P) and force ratio,
Ξ΅P = (J~PΒ·ΞpG~P)/-(JO2PΒ·ΞkGO2) = ~P/P β ΞpG~P/-ΞkGO2 = jβP β fβP (2)
The upper limit of ~P/P is the mechanistic ~P:O2 ratio or stoichiometric number, Ξ½~P/O2. The free respiratory OXPHOS capacity, βP=P-L, is potentially available to drive phosphorylation, ~P (Figure 1). Quantitatively justified in cases [3] but better adjusted to the protonmotive force, Ξpmt, the dissipative LEAK component, L, in the OXPHOS state P can be assessed by respiration, L, measured in the LEAK state,
Ξ½~P/O2 = ~Plimit/P = ~P/(P-L) = ~P/βP (3)
~P/P divided by ~P/βP defines the OXPHOS coupling efficiency, jβP, as a normalized flux ratio, which is a hyperbolic function of RCR (Figure 2),
jβP = βP/P = (L-P)/P = 1-L/P = 1-RCR-1 (4)
References and acknowledgements
Supported by K-Regio project MitoCom Tyrol.
- Pesta D, Gnaiger E (2012) High-resolution respirometry. OXPHOS protocols for human cells and permeabilized fibres from small biopisies of human muscle. Methods Mol Biol 810: 25-58.