Wikström M, Krab K
J Bioenerg Biomembr. 1986 Jun;18(3):181-93. doi: 10.1007/BF00743463.
The Q cycle and the b cycle are the main current models of action of the cytochrome bc-type complexes of mitochondria, bacteria, and chloroplasts. Both are based on the concept, proposed in 1972, of two sequential one-electron oxidations of (ubi)quinol along two discrete pathways which operate at different redox potentials, and with bound semiubiquinone as an intermediate. The models differ in two respects, viz. in the pathway of electron transfer and the principle of linkage of electron transfer to proton translocation. In this article we outline a new model, called the semiquinone or, simply, SQ cycle, which is based on the electron transfer principles of the b cycle but which incorporates the Q cycle concept of direct coupling between electron transfer and proton translocation through action of ubiquinone.
Q循环和b循环是目前关于线粒体、细菌和叶绿体中细胞色素bc型复合物作用的主要模型。两者都基于1972年提出的概念，即（泛）醌醇沿着两条在不同氧化还原电位下运行的离散途径进行两个连续的单电子氧化，并以结合的半醌作为中间体。这两个模型在两个方面有所不同，即电子传递途径以及电子传递与质子转运的偶联原理。在本文中，我们概述了一种新模型，称为半醌模型或简称为SQ循环，它基于b循环的电子传递原理，但通过泛醌的作用纳入了电子传递与质子转运直接偶联的Q循环概念。
