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State 2

From Bioblast


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State 2

Description

ROX.jpg 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. The peak โ€“ supported by endogenous substrates โ€“ is, therefore, a pre-steady state phenomenon preceding State 2. 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: Chance 1955 JBC-III, Gnaiger 2014 MitoPathways


MitoPedia concepts: Respiratory state 






State 2: towards a concept-linked terminology of respiratory states

State 2 is equivalent to residual oxygen consumption, ROX. We have sought independent controls on whether State 2 corresponds to complete oxidation of the system. It is logical that this be so, for respiration is zero in State 2 because substrate, not phosphate acceptor, is limiting (Chance and Williams 1955).

A numerical sequence of respiratory states has been introduced by Chance and Williams. The State 2 and 4 terminology, however, has become confusing and misunderstood: โ€˜.. the controlled respiration prior to addition of ADP, which is strictly termed โ€œstate 2โ€, is functionally the same as state 4, and the latter term is usually used for both statesโ€™ (Nicholls and Ferguson 1992). Alchemy has a tradition of using the same term for multiple meanings and different terms for the same. A termonological extension from integers to the fraction 3ยฝ has been suggested to indicate an intermediate mitochondrial energy state somewhere between States 3 and 4. Paradoxically, a fractional numbering system (real numbers of mathematics) would suggest that ADP-activated hypoxia were intermediate between States 3.0 and 5.0, i.e. State 4.0. This state of terminology requires fundamental reconsideration for clarification, particularly for extending bioenergetics to mitochondrial respiratory physiology and OXPHOS analysis.