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 Q (CoQ or ubiquinone) in mitochondria or plastoquinones in the photosynthetic system. Originally, the concept 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 QH₂) binds to the Q_o site of CIII, while the oxidized CoQ (ubiquinone Q) to the Q_i site of CIII. First, QH₂ reduces the iron-sulfur protein and feeds cytochrome c₁ with one electron. The other electron is transferred to the b_L heme and reduces the b_H heme, which transfers the electron to ubiquinone at the Q_i-site which is reduced to a semiquinone. A second QH₂ 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 Q_i-site can be reused by binding to the Q_o-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

Bioblast links: Q - >>>>>>> - Click on [Expand] or [Collapse] - >>>>>>>

Coenzyme Q

» Coenzyme Q

» Quinone, Ubiquinone Q; oxidized

» Quinol, Ubiquinol QH₂; reduced

» Semiquinone

» Coenzyme Q2

» Q-redox state

» Q-pools

Mitochondrial pathways, respiratory Complexes, and Q

» Q-cycle

» Q-junction

» Convergent electron flow

» NS-pathway

» FNS

» FNSGp

» N-pathway

» Reverse electron flow from CII to CI

» CI

» Rotenone

» Amytal

» Piericidin

» S-pathway

» CII

» Malonate

» F-pathway

» CETF, Electron-transferring flavoprotein complex

» Gp-pathway

» CGpDH, Glycerophosphate dehydrogenase complex

» CIII

» Myxothiazol

» Choline dehydrogenase

» Dihydro-orotate dehydrogenase

NextGen-O2k and Q-Module

» NextGen-O2k

» Q-Module

» Q-Sensor

» Cyclic voltammetry

» Three-electrode system

General

» Categories of SUIT protocols

» Electron transfer pathway

» Electron-transfer-pathway state

» F-junction

» N-junction

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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 Q (CoQ or [[ubiquinone]]) in mitochondria or plastoquinones in the photosynthetic system. Originally, the concept 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 ([[quinol |ubiquinol]] QH<sub>2</sub>) binds to the Q<sub>o</sub> site of CIII, while the oxidized CoQ ([[ubiquinone]] Q) to the Q<sub>i</sub> site of CIII.  First, QH<sub>2</sub> reduces the iron-sulfur protein and feeds cytochrome ''c''<sub>1</sub> 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 Q<sub>i</sub>-site which is reduced to a [[semiquinone]]. A second QH<sub>2</sub> 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 Q<sub>i</sub>-site can be reused by binding to the Q<sub>o</sub>-site of CIII.
-|info=[[Mitchell 1975 FEBS Letters]]
+|info=[[Crofts 2004 Annu Rev Physiol]], [[Hunte 2003 FEBS Letters]], [[Mitchell 1975 FEBS Letters]], [[Trumpower 1990 J Biol Chem]], [[Trumpower 1994 Annu Rev Biochem]]
 }}
+{{Template:Keywords: Q}}