Transducing Functions of Mitochondria

Abstract

The arrangements of the respiratory chain components of mitochondria which are most generally accepted at this time are summarized in Fig. 10. This scheme includes cytochromes a₃, a, c, c₁, and b and in addition flavoprotein and coenzyme Q. Cytochrome b is thought to be present as two and most probably three spectrographically distinct species (e.g., Wikström 1973). Two of these have been designated b_K and b_T (Chance et al. 1970). The experimental evidence for this scheme together with the properties of the system have been reviewed repeatedly (e.g., Chance and Williams 1956, Lehninger 1965, and Klingenberg 1968). This scheme has been derived in part from spectroscopic data together with kinetic studies and data on the effects of a variety of inhibitors. In part it is based on the study of the redox properties of the various components and the dissection of the mitochondria by various disruptive procedures. The approaches making use of disruption and reconstitution have been examined in the thorough review of Kagawa (1972). The more recent application of EPR techniques has permitted the identification of a number of iron-sulfur proteins which play a role in the respiratory chain (see Ohrme-Johnson et al. 1973, and Ohnishi et al. 1970, 1971, 1972 a, b). The arrangement of these iron-sulfur proteins is illustrated in Fig. 11 (Ohnishi 1973). The iron-sulfur proteins have been designated centers 1 to 9. Center 1 is actually constituted of two separate but very similar proteins desginated 1 a and 1 b. Two of the iron-sulfur proteins are associated with succinic dehydrogenase and another (center 9) is the iron-sulfur protein of Rieske (Rieske et al. 1964 a, b).