Difference between revisions of "Q-cycle"
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'''Q-cycle''' refers to the sequential oxidation and reduction of the electron carrier Coenzyme | '''Q-cycle''' refers to the sequential oxidation and reduction of the electron carrier Coenzyme Q (CoQ or [[ubiquinone]]) in mitochondria or plastoquinones in the photosynthetic system. Originally, the idea of the Q-cycle was proposed by [[Mitchell P|Peter D. Mitchell]]. Following several modifications, the Q-cycle is established, describing how [[CIII]] translocates hydrogen ions against the protonmotive force. The reduced CoQ (ubiquinol) binds to the Qo site of CIII, while the oxidized CoQ ([[ubiquinone]]) to the Qi site of CIII. First, ubiquinol reduces the iron-sulfur protein and feeds cytochrome ''c''1 with one electron. The other electron is transferred to the ''b''<sub>L</sub> heme and reduces the ''b''<sub>H</sub> heme, which transfers the electron to ubiquinone at the Qi-site which is reduced to a [[semiquinone]]. A second ubiquinol is required to fully reduce semiquinone to ubiquinol. At the end of the Q-cycle, four protons leave the mt-matrix and enter the intermembrane space, and the reduced cytochrome ''c'' transfers electrons to CIV. The ubiquinol generated at the Qi-site can be reused by binding to the Qo-site of CIII. | ||
|info=[[Crofts 2004 Annu Rev Physiol]], [[Hunte 2003 FEBS Letters]], [[Mitchell 1975 FEBS Letters]], [[Trumpower 1990 J Biol Chem]], [[Trumpower 1994 Annu Rev Biochem]] | |info=[[Crofts 2004 Annu Rev Physiol]], [[Hunte 2003 FEBS Letters]], [[Mitchell 1975 FEBS Letters]], [[Trumpower 1990 J Biol Chem]], [[Trumpower 1994 Annu Rev Biochem]] | ||
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Revision as of 17:58, 11 March 2021
- high-resolution terminology - matching measurements at high-resolution
Q-cycle
Description
Q-cycle refers to the sequential oxidation and reduction of the electron carrier Coenzyme Q (CoQ or ubiquinone) in mitochondria or plastoquinones in the photosynthetic system. Originally, the idea of the Q-cycle was proposed by Peter D. Mitchell. Following several modifications, the Q-cycle is established, describing how CIII translocates hydrogen ions against the protonmotive force. The reduced CoQ (ubiquinol) binds to the Qo site of CIII, while the oxidized CoQ (ubiquinone) to the Qi site of CIII. First, ubiquinol reduces the iron-sulfur protein and feeds cytochrome c1 with one electron. The other electron is transferred to the bL heme and reduces the bH heme, which transfers the electron to ubiquinone at the Qi-site which is reduced to a semiquinone. A second ubiquinol is required to fully reduce semiquinone to ubiquinol. At the end of the Q-cycle, four protons leave the mt-matrix and enter the intermembrane space, and the reduced cytochrome c transfers electrons to CIV. The ubiquinol generated at the Qi-site can be reused by binding to the Qo-site of CIII.
Abbreviation: Q
Reference: Crofts 2004 Annu Rev Physiol, Hunte 2003 FEBS Letters, Mitchell 1975 FEBS Letters, Trumpower 1990 J Biol Chem, Trumpower 1994 Annu Rev Biochem
