Description

LEAK respiration or LEAK oxygen flux, L, compensating for proton leak, proton slip, cation cycling and electron leak, is measured as mitochondrial respiration in the LEAK state, in the presence of reducing substrate(s), but absence of ADP (theoretically, absence of inorganic phosphate presents an alternative), or after enzymatic inhibition of the phosphorylation system. In this non-phosphorylating resting state, the electrochemical proton gradient is increased to a maximum, exerting feedback control by depressing oxygen flux to a level determined by the proton leak and the H⁺/O ratio. In this state of maximum protonmotive force, LEAK respiration is higher than the LEAK component in state P (OXPHOS capacity).

Abbreviation: L

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

MitoPedia methods: Respirometry

MitoPedia topics: "Respiratory state" 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 state"Respiratory state" 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.

Gnaiger E (2014) The LEAK state of respiration: towards a concept-linked terminology of respiratory states. Mitochondr Physiol Network 2014-04-20.

OROBOROS (2014) Mitochondr Physiol Network

Abstract: Mitochondrial respiratory states have been defined originally by Chance and Williams (1955) as a sequence (from 1 to 5) of titrations and transitions in a respiratory protocol, including State 4 as a LEAK state of respiration obtained after exhaustion of the added ADP. The second state (State 2) is induced by addition of 'high ADP'. Confusion persists in the current literature as to the meaning of State 2, which can be resolved by a transition from a specific protocol-linked to a generalized concept-linked terminology.

• O2k-Network Lab: AT Innsbruck Gnaiger E

Labels:

Regulation: Coupling efficiency;uncoupling Coupling state: LEAK, ETS"ETS" is not in the list (LEAK, ROUTINE, OXPHOS, ET) of allowed values for the "Coupling states" property.

HRR: Theory

The LEAK state of respiration: towards a concept-linked terminology of respiratory states

State 2: an alternative protocol

Sequential addition of (1) mitochondria, (2) ADP, and (3) reduced substrates is the basis of the original State 1-2-3 definitions of respiratory states (Chance and Williams 1955 part III, 1956), where State 2 is zero respiration or residual oxygen consumption in the absence of substrate. An alternative protocol is well established, as shown e.g. by the classical Fig. 5A (Chance and Williams 1955 part I): 600 µM ADP is added after a state described as ‘Aerobic mitochondria plus succinate’. That state was never defined as ‘State 2’ by Brit Chance. Later Estabrook (1967) made this protocol more popular, with addition of substrate before any ADP or ATP was added.

In this alternative protocol, a respiratory LEAK state is induced as the second respiratory state of isolated mitochondria, permeabilized tissues, or permeabilized cells, adding the mitochondrial preparation to respiration medium containing inorganic phosphate (State 1), then adding reduced substrate (no external adenylates). This second state (Estabrook 1967) is a non-phosphorylating LEAK state, L_N (N for no adenylates; Gnaiger 2009), when substrate-saturated respiration compensates for the proton leak (mainly) in the absence of ADP.

In contradiction to the original definition of State 2 (ROX), yet with reference to Chance and Williams (1956), 'State 2' has later been used for describing this functionally different state of LEAK respiration:

‘State 2: substrate added, respiration low due to lack of ADP. .. the controlled respiration prior to addition of ADP, which is strictly termed “state 2”, is functionally the same as state 4, and the latter term is usually used for both states’ (Nicholls & Ferguson 1992).

To overcome the termonological confusion persisting in the scientific literature, the respiratory coupling states of LEAK respiration, OXPHOS capacity and ETS capacity are distinguished from residual oxygen consumption (ROX; Gnaiger 2009).

References

Chance B, Williams GR (1955) Respiratory enzymes in oxidative phosphorylation. I. Kinetics of oxygen utilization. J Biol Chem 217: 383-393.

Chance B, Williams GR (1955) Respiratory enzymes in oxidative phosphorylation. III. The steady state. J Biol Chem 217: 409-427.

Chance B, Williams GR (1956) The respiratory chain and oxidative phosphorylation. Adv Enzymol 17: 65-134.

Estabrook R (1967) Mitochondrial respiratory control and the polarographic measurement of ADP:O ratios. Methods Enzymol 10: 41-47.

Gnaiger E (2009) Capacity of oxidative phosphorylation in human skeletal muscle. New perspectives of mitochondrial physiology. Int J Biochem Cell Biol 41: 1837–1845. PMID: 19467914

Nicholls DG, Ferguson SJ (2002) Bioenergetics 3. Academic Press, London. 287 pp.