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State 2

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State 2

Description

Substrate limited state of residual oxygen consumption, after addition of ADP to isolated mitochondria suspended in mitochondrial respiration medium in the absence of reduced substrates (ROXD). Residual endogenous substrates are oxidized during a transient stimulation of oxygen flux by ADP. Subsequently oxygen flux declines to a low level (or zero) at the steady State 2 (Chance and Williams 1955). ADP concentration (D) remains high during ROXD.

Abbreviation: ROXD

Reference: MiPNet12.15, Chance 1955 JBC-III


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Preparation: Isolated Mitochondria"Isolated Mitochondria" is not in the list (Intact organism, Intact organ, Permeabilized cells, Permeabilized tissue, Homogenate, Isolated mitochondria, SMP, Chloroplasts, Enzyme, Oxidase;biochemical oxidation, ...) of allowed values for the "Preparation" property., Permeabilized Cell or Tissue; Homogenate"Permeabilized Cell or Tissue; Homogenate" is not in the list (Intact organism, Intact organ, Permeabilized cells, Permeabilized tissue, Homogenate, Isolated mitochondria, SMP, Chloroplasts, Enzyme, Oxidase;biochemical oxidation, ...) of allowed values for the "Preparation" property. 

Regulation: Respiratory state"Respiratory state" is not in the list (Aerobic glycolysis, ADP, ATP, ATP production, AMP, Calcium, Coupling efficiency;uncoupling, Cyt c, Flux control, Inhibitor, ...) of allowed values for the "Respiration and regulation" property., Respiration; OXPHOS; ETS Capacity"Respiration; OXPHOS; ETS Capacity" is not in the list (Aerobic glycolysis, ADP, ATP, ATP production, AMP, Calcium, Coupling efficiency;uncoupling, Cyt c, Flux control, Inhibitor, ...) of allowed values for the "Respiration and regulation" property. 




An alternative protocol

Whereas sequential addition of (1) mitochondria, (2) ADP, and (3) reduced substrates is the basis of the original State 1-2-3 definitions or respiratory states (Chance and Williams 1955 part III, 1956), 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 explicit contradiction to the original definition of State 2 (zero respiration or residual oxygen consumption in the absence of substrate), this term has later been used for describing a functionally different state (http://www.bioblast.at/index.php/Talk:State_2): ‘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’ (Bioenergetics. Nicholls & Ferguson 1992).


Insufficiently concerned of clarity of concepts and historical correctness, many authors published on State 2 in this confused state of terminology.

In contrast to the definition of State 2 by Chance and Williams (1955, 1956), a respiratory LEAK state may be induced as the second respiratory state in a protocol with 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, LN (N for no adenylates; Gnaiger 2009), when substrate-saturated respiration compensates for the proton leak (mainly) in the absence of ADP. State 2 (Chance and Williams 1955), however, is defined as high [ADP] without external substrates, followed by State 3 induced by addition of reduced substrate(s).

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