- high-resolution terminology - matching measurements at high-resolution
Q-cycle
Description
in preparation 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 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 (Trumpower BL 1990 and 1994, Hunte C at al 2003).
Abbreviation: Q
Reference: Mitchell 1975 FEBS Letters
