Oxygen kinetics

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Oxygen kinetics

Description

Oxygen kinetics describes the dependence of respiration of isolated mitochondria or cells on oxygen partial pressure. Frequently, a strictly hyperbolic kinetics is observed, with two parameters, the oxygen pressure at half-maximum flux, p50, and maximum flux, Jmax. The p50 is in the range of 0.2 to 0.8 kPa for cytochrome c oxidase, isolated mitochondria and small cells, strongly dependent on Jmax and coupling state.


Reference: Scandurra 2010 Adv Exp Med Biol


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Last update: 2019-11-11

Oxygen dependence of respiration

In isolated mitochondria and many types of small cells (such as endothelial cells, fibroblasts etc), zero-order kinetics with respect to oxygen pressure (i.e., independence of flux with declining oxygen concentration) applies over a wide range down to very low oxygen levels, where then a hyperbolic oxygen dependence is observed. With a p50 (c50, apparent Km) in the order of <1 Β΅M and a hyperbolic oxygen dependence of flux, 99 % saturation of flux and hence zero-order kinetics is observed at an oxygen concentration >19 Β΅M (i.e., >2 kPa, >2 % oxygen saturation or >10 % air saturation). For reviews see Gnaiger et al 1995, Scandurra and Gnaiger 2010.
Compared to the difficulties with classical chart recorder tracings, our 'modern' approaches over the past 20 years allowed us to drop the linearity assumption and statistically test for it, frequently rejecting this assumption to describe a non-linear oxygen dependence beyond the low-oxygen range governed by cytochrome c oxidase. For review see Gnaiger 2003.
In permeabilized muscle fibers (30 to 37 Β°C), oxygen kinetics is shifted 100-fold due to artificially high oxygen gradients, forcing us to apply elevated oxygen levels for obtaining near-zero-order kinetics.

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References

  • Gnaiger E (2001) Bioenergetics at low oxygen: dependence of respiration and phosphorylation on oxygen and adenosine diphosphate supply. Respir Physiol 128:277-97. - Β»Bioblast linkΒ«

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