State 3

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State 3


P.jpg State 3 respiration is the ADP stimulated respiration of isolated coupled mitochondria in the presence of high ADP and Pi concentrations, supported by a defined substrate or substrate combination at saturating oxygen levels (Chance and Williams, 1955). State 3 respiration can also be induced in permeabilized cells, including permeabilized tissue preparations and tissue homogenates. ADP concentrations applied in State 3 are not necessarily saturating, whereas OXPHOS capacity is measured at saturating concentrations of ADP and Pi (OXPHOS state). For instance, non-saturating ADP concentrations are applied in State 3 in pulse titrations to determine the P/O ratio in State 3→4 (D→T) transitions, when saturating ADP concentrations would deplete the oxygen concentration in the closed oxygraph chamber before State 4 is obtained (Gnaiger et al 2000; Puchowicz et al 2004). Respiration in the OXPHOS state or in State 3 is well coupled, and partially uncoupled (physiological) or partially dyscoupled (pathological). A high mt-membrane potential provides the driving force for oxidative phosphorylation, to phosphorylate ADP to ATP and to transport ADP and ATP across the mitochondrial inner membrane (mtIM) through the adenine nucleotide translocase (ANT). The mt-membrane potential is reduced, however, in comparison to the LEAK state of respiration, whereas the cytochromes are in a more oxidized redox state.

Abbreviation: P

Reference: Chance 1955 JBC-III, Gnaiger 2020 BEC MitoPathways

MitoPedia concepts: Respiratory state, Find 

MitoPedia topics: EAGLE 

Communicated by Gnaiger E 2010-08-15, edited 2017-04-18, 2014-06-23.

Maximum oxygen flux in State 3 ?

Oxygen flux is not necessarily 'maximum' in State 3 for different reasons:
  • Concentrations of ADP and inorganic phosphate (Pi) are high but may not be saturating (kinetic limitation) leading to underestimation of OXPHOS capacity and overestimation of excess E-P capacity.
  • The substrate or substrate combination may not support the physiological maximum flux through the electron transfer-pathway (ET-pathway), particularly due to electron gating of mitochondrial pathways converging at the Q-junction (limitation due to pathway control).
  • OXPHOS capacity is less than ET capacity in coupled mitochondria with limiting phosphorylation system capacity (limitation by the enzymatic capacity of utilizating the electrochemical proton gradient).
  • The definition of State 3 lacks a fundamental attribute of OXPHOS capacity. 'High ADP' is a concentration of ADP specifically selected to allow measurememt of a State 3 to State 4 transition of isolated mitochondria in a closed respirometric system. Starting at oxygen levels near air saturation, the 'high ADP' concentration added must be low enough to allow phosphorylation to ATP at a coupled oxygen consumption that does not lead to complete oxygen depletion during the transition to State 4.
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