Cytochrome b-565 in Saccharomyces cerevisiae: use of mutants in the cob- box region of the mitochondrial DNA to study the functional role of this spectral species of cytochrome b. 2. Relationship between energetic data and cytochrome b-565 content.

A wild-type strain of Saccharomyces cerevisiae and temperature-dependent revertants of isonuclear box mutants partially or completely devoid of cytocheomr b-565, were used to study the role of this cytochrome in oxidative phosphorylation. At the mitochondrial level, the phosphorylating data and the succinate oxidase activity at three different temperatures (16 degrees C, 28 degrees C and 36 degrees C) were measured in these strains showing various cytochrome b-565 contents. It is concluded that this cytochrome b-565 is not in the main pathway of the electron transfer chain. At the optimum growth temperature (28 degrees C), the measurements of the P/O ratio for the wild phenotype strains, with ethanol as substrate, led to the conclusions that two phosphorylation sites of the respiratory chain are functional in these strains. The growth yields for wild phenotype strains and revertants grown in vivo in complex media, with ethanol or galactose as the energy source (at 16 degrees C, 28 degress C and 36 degrees C), were compared with the cytochrome b-565 content. The growth yields showed small variations if compared to the reference strain, when the cytochrome b-565 content was greatly diminished or absent. Thus the ATP production at side II is independent of the cytochrome b-565 content. Cytochrome b-565 does not play an essential role in oxidative phosphorylation.