Spectral properties of cytochrome b-561 and cytochrome b-565 in mucidin-resistant mutants of Saccharomyces cerevisiae.

The oxidation of NADH in submitochondrial particles isolated from MUC1, MUC2 and MUC3 mucidin-resistant mutants of Saccharomyces cerevisiae is specifically resistant to mucidin. Extra reduction of cytochrome b-565 induced by mucidin is demonstrated in all tested mucidin-resistant mutants. Red shift of cytochrome b-561 is induced by mucidin in two independent MUC3 mutants. In MUC1 and MUC2 mutants, the red shift is not induced by mucidin, while that promoted by antimycin A and 2-n-heptyl-4-hydroxyquinoline N-oxide are normal. It is concluded that the extra reduction of cytochrome b-565 and the red shift of cytochrome b-561 elicited by mucidin can be largely dissociated from the overall inhibition of the electron flow by distinct mucidin-resistant mutations in different exons of the split mitochondrial gene of cytochrome b.