Gnaiger 2002 Biochem Soc Trans

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Gnaiger E, Kuznetsov AV (2002) Mitochondrial respiration at low levels of oxygen and cytochrome c. Biochem Soc Trans 30:242-8.

» PMID: 12023860 Open Access

Gnaiger E, Kuznetsov AV (2002) Biochem Soc Trans

Abstract: In the intracellular microenvironment of active muscle tissue, high rates of respiration are maintained at near-limiting oxygen concentrations. The respiration of isolated heart mitochondria is a hyperbolic function of oxygen concentration and half-maximal rates were obtained at 0.4 and 0.7 µM O2 with substrates for the respiratory chain (succinate) and cytochrome c oxidase [N,N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride (TMPD)ascorbate] respectively at 30 °C and with maximum ADP stimulation (OXPHOS).

The respiratory response of cytochrome c-depleted mitoplasts to external cytochrome c was biphasic with TMPD, but showed a monophasic hyperbolic function with succinate. Half-maximal stimulation of respiration was obtained at 0.4 µM cytochrome c, which was nearly identical to the high-affinity Km' for cytochrome c of cytochrome c oxidase supplied with TMPD. The capacity of cytochrome c oxidase in the presence of TMPD was 2-fold higher than the capacity of the respiratory chain with succinate, measured at environmental normoxic levels. This apparent excess capacity, however, is significantly decreased under physiological intracellular oxygen conditions and declines steeply under hypoxic conditions. Similarly, the excess capacity of cytochrome c oxidase declines with progressive cytochrome c depletion. The flux control coeficient of cytochrome c oxidase, therefore, increases as a function of substrate limitation of oxygen and cytochrome c, which suggests a direct functional role for the apparent excess capacity of cytochrome c oxidase in hypoxia and under conditions of intracellular accumulation of cytochrome c after its release from mitochondria.

O2k-Network Lab: AT Innsbruck Gnaiger E, AT Innsbruck Oroboros

Labels: MiParea: Respiration 

Organism: Rat  Tissue;cell: Heart  Preparation: Isolated mitochondria, SMP 

Regulation: Cyt c, Flux control, Oxygen kinetics, Threshold;excess capacity  Coupling state: OXPHOS  Pathway: S, CIV  HRR: Oxygraph-2k