Electron transport system

The term electron transfer chain (or electron transport chain, ETC) is a misnomer. Understanding mitochondrial respiratory control has suffered greatly from this inappropriate terminology, although textbooks using the term ETC (Lehninger 1970; Nicholls & Ferguson 2002) make it sufficiently clear that electron transfer systems are not arranged as a chain: the „ETC‟ is in fact not a simple chain but an arrangement of electron transfer complexes in a non-linear, convergent electron transfer system (Hatefi et al 1962; ETS). The firmly established convention of defining the electron transfer chain as being comprised of four Complexes has conceptual weaknesses. (a) In fact, there are at least six Complexes of mitochondrial electron transfer: In addition to Complexes I and II, glycerophosphate dehydrogenase (GpDH) and electron transferring flavoprotein (ETF) are involved in electron transfer to Complex III. (b) The term „chain‟ suggests a linear sequence, whereas the functional structure of the electron transfer system can only be understood by recognizing the convergence of electron flow at the Q-junction, followed by a chain of Complexes III and IV, mediated by [cytochrome c]. Electrons flow to oxygen from either Complex I with a total of three coupling sites, or from Complex II and other flavoproteins, providing multiple entries into the Q-cycle with two coupling sites downstream. MiPNet11.04