The mitochondrial respiratory chain and ATP synthase complexes: Composition, structure and mutational studies

The oxidative phosphorylation process is dependent on the assembly of both the respiratory chain that generates the electrochemical potential of the mitochondrial inner membrane and the ATP synthase complex which uses this membrane potential to drive ATP synthesis. The five respiratory enzymes involved in this process, complexes I to V, are composed of multiple subunits, some of which are synthesized on mitochondrial ribosomes, whereas others are a product of the nucleocytoplasmic genetic system. The mitochondrial genome has a limited coding capacity and the co-ordinate expression of all the subunits forming these complexes has been shown to be under nuclear control. Present knowledge of complexes I to V mainly comes from studies of bovine and fungal mitochondria. If beef heart mitochondria represent a choice material for studying the composition and structure of these complexes, Saccharomyces cerevisiae and Neurospora crassa and their numerous respiratory mutants, are ideal organisms for investigating the co-ordination of nuclear and mitochondrial genomes in their assembly. The major reason for the interest in respiratory complexes and ATP synthase from the mitochondrial inner membrane in Homo sapiens and in higher plants is the relationship between enzyme deficiencies and human diseases and ageing on one hand, and such plant phenotypic abnormalities as cytoplasmic male sterility on the other.