Difference between revisions of "Q-cycle"

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Q-cycle

Description

Q-cycle refers to the sequential oxidation and reduction of the electron carrier Coenzyme Q10 (CoQ10 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 CoQ10 (ubiquinol) binds to the Qo site of CIII, while the oxidized CoQ10 (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 b_H 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 Physio, Hunte 2003 FEBS Letters, Mitchell 1975 FEBS Letters, Trumpower 1990 J Biol Chem, Trumpower 1994 Annu Rev Biochem

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 {{MitoPedia
 |abbr=Q
-|description= ''in preparation''
+|description=
-'''Q-cycle''' refers to the sequential oxidation and reduction of the electron carrier Coenzyme Q10 (CoQ10 or ubiquinone) in mitochondria or of plastoquinones in the photosynthetic system. Originally, the idea of the Q-cycle was proposed by Peter D. Mitchell and today is accepted as the concept of how CIII moves protons after several modifications (Trumpower BL 1990, 1994; review see Crofts AR 2004). The reduced CoQ10 (ubiquinol) binds to the Qo site of CIII, while the oxidized CoQ10 (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 bL 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 (Trumpower BL 1990 and 1994, Hunte C at al 2003).
+'''Q-cycle''' refers to the sequential oxidation and reduction of the electron carrier Coenzyme Q10 (CoQ10 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 CoQ10 (ubiquinol) binds to the Qo site of CIII, while the oxidized CoQ10 ([[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 bL 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=[[Mitchell 1975 FEBS Letters]]
+|info=[[Crofts 2004 Annu Rev Physio]], [[Hunte 2003 FEBS Letters]], [[Mitchell 1975 FEBS Letters]], [[Trumpower 1990 J Biol Chem]], [[Trumpower 1994 Annu Rev Biochem]]
 }}