Oxidative phosphorylation in cardiolipin-lacking yeast mitochondria

The role of cardiolipin in mitochondrial energy transformation was studied by comparing oxidative phosphorylation in the Saccharomyces cerevisiae cardiolipin synthase null mutant crd1Delta, and in isogenic wild type. Oxygen consumption experiments and membrane potential kinetics during the phosphorylation cycle in isolated mitochondria indicated that the absence of cardiolipin causes only a moderate deficiency of mitochondrial energy-transforming machinery at 25 degrees C. However, at 40 degrees C, respiration was completely uncoupled from phosphorylation for the mutant mitochondria, in contrast with that for the wild-type. Membranepotential kinetics demonstrated an increased susceptibility of the mutant mitochondria to gradual deterioration during in vitro incubation. These results suggest that cardiolipin, although normally associated with several of the major enzymes of oxidative phosphorylation and required in vitro for their maximal activity, is not absolutely necessary for mitochondrial energy transformation under optimal conditions. The role of cardiolipin is, rather, to improve efficiency of oxidative phosphorylation and its resistance to unfavourable conditions, such as increased temperature.