The components of the respiratory chain

Abstract

The respiratory chain of eukaryotic organisms is located on the inner membrane of the mitochondrion (Section 3,1) and principally catalyses the oxidation of NAD(P)H and succinate (together with minor substrates such as glycerol-3-phosphate, fattyacyl-CoA) by molecular oxygen. It is an aggregate of four discrete redox carrier complexes (I, II, III and IV) plus transhydrogenase, ubiquinone and cytochrome c. The redox carriers can be monitored by a variety of spectroscopic techniques, and the latter have historically been used to analyse the respiratory membrane in situ. These spectroscopic approaches have more recently been supplemented with increasingly sophisticated methods for (i) gently solubilizing the respiratory chain complexes (using either anionic detergents such as cholate or deoxycholate in the presence of KCl, or nonionic detergents such as Triton X-100), (ii) resolving these complexes into their constituent enzymes and redox carriers (using chaotropic agents such as Perchlorate), and (iii) investigating the oligomeric nature of many of the apoproteins (using Polyacrylamide gel electrophoresis in the presence of dissociating agents such as sodium dodecyl sulphate; SDS-PAGE) [4–9]. It is pertinant at this point, therefore, to examine in some detail the redox and molecular properties of the individual redox carriers and their aggregated complexes, as well as some of the substrates, in order to appreciate fully the complicated nature of the respiratory chain.