P/E control ratio

high-resolution terminology - matching measurements at high-resolution

P/E control ratio

Description

The phosphorylation system control ratio or OXPHOS/ETS (P/E) ratio is an expression of the limitation of OXPHOS capacity by the phosphorylation system. The P/E ratio increases with increasing capacity of the phosphorylation system up to a maximum of 1.0 when it matches or is in excess of ETS capacity. P/E also increases with uncoupling. P/E increases from the lower boundary set by L/E (zero capacity of the phosphorylation system), to the upper limit of 1.0, when there is no limitation of P by the phosphorylation system or the proton backpressure (capacity of the phosphorylation system fully matches the ETS capacity; or if the system is fully uncoupled). It is important to separate the kinetic effect of ADP limitation from limitation by enzymatic capacity at saturating ADP concentration.

Abbreviation: P/E

Reference: Gnaiger 2012 MitoPathways, Gnaiger 2009 Int J Biochem Cell Biol, Pesta 2012 Methods Mol Biol

MitoPedia methods: Respirometry 

MitoPedia topics: "Respiratory control ratio" is not in the list (Enzyme, Medium, Inhibitor, Substrate and metabolite, Uncoupler, Sample preparation, Permeabilization agent, EAGLE, MitoGlobal Organizations, MitoGlobal Centres, ...) of allowed values for the "MitoPedia topic" property. Respiratory control ratio"Respiratory control ratio" is not in the list (Enzyme, Medium, Inhibitor, Substrate and metabolite, Uncoupler, Sample preparation, Permeabilization agent, EAGLE, MitoGlobal Organizations, MitoGlobal Centres, ...) of allowed values for the "MitoPedia topic" property. 

P/E from mouse to man

When using animal (specifically mouse) versus human muscle tissue, it is important to be aware of the fact that human muscle shows a significant apparent excess capacity of the ETS versus the phosphorylation system with physiological substrate combinations (P/E<1.0), in contrast to mouse skeletal and cardiac tissue (P/E=0.97 to 1.0). Therefore, uncoupler titrations (to estimate ETS capacity, E) following ADP stimulation (to estimate OXPHOS capacity, P) are different: The optimum uncoupler concentration can be estimated by stepwise titration from the P state to the E state in human muscle mitochondria. In mouse muscle mitochondria, this is not possible if P/E=1.0, since under these respiratory control conditions there is no stimulation of respiration at any uncoupler concentration, but only inhibition at increasing uncoupler concentrations.

To show the actual action of the uncoupler in such mitochondria, a control experiment must be carried out when titrating uncoupler in the absence of ADP, to see the actual stimulation from the LEAK state (L) to the ETS state (E).

Can P/E be higher than 1.0?

OXPHOS capacity can be less than or equal to ETS capacity, but it cannot be higher. Any result giving P/E>1.0 is due to an experimental artefact. Such an artefact may be obtained due to application of an inhibitory uncoupler concentration, or inhibition of ETS by inhibitors of a component of the phosphorylation system.

• The P/E ratio is also discussed in: ETS capacity

Biochemical coupling efficiency: from 0 to <1

• More details: Biochemical coupling efficiency