1. A respiratory-deficient mutant strain of yeast was obtained from wild strain of Saccharomyces servisiae by treatment with 4-nitroquinoline N-oxide. Ultrastructure and function of the wild or mutant strains and the mitochondrial fractions isolated from these strains were examined by biochemical and electron microscopic analyses.
2. The frequency of the respiratory-deficient mutant strain in yeast induced with 10-6M 4-nitroquinoline N-oxide was about 40 %. 3. Respiratory-deficient mutant strain is incapable of reducing 2, 3, 5-triphenyltetrazolium chloride salt and to grow on lactate medium. In addition to this, the mutant has been found to have lost its ability to take up oxygen in sodium succinate and pyruvate. 4. 4.Nitroquinoline N-oxide in the concentration that induces a mutant of yeast cells or its kin inhibits the oxygen uptake in normal strain. 5. The normal strain of yeast is characterized by difference spectrum corresponding to cytochromes a+as, band c+Cll respectively, whereas,
the mutant strain containes almost no cytochromes a+ as, band C1 but contains normal or increased amount of cytochrome c. 6. Mitochondrial fraction isolated from mutant strain has largely lost its ability to oxidize succinate. On the other hand, NADH-, lactate-and
cytochrome c-oxidase activities are reduced by about 1/17, 1/7 and 1/8 of that of normal strain, respectively.
7. Succinate dehydrogenase activity of mutant strain is almost zero. Moreover, this activity is not affected on the addition of phenazine methosulfate. NADH dehydrogenase activity of mutant stran is about 1/2 of normal strain.
8. The variations in mitochondrial structure of normal and mutant strain in the stationary phase have been followed with the aid of electron microscopy. In contrast to the normal strain, the mutant strain revealed distinct morphological changes in mitochondria, especially, the lack of cristae in its interior. The results have been interpreted to indicate that the mutant induced by 4.nitroquinoline N.oxide has a character of cyto. plasmic mutant.</p
