Presence of Cytochrome c₁ in Cytoplasmic “Petite” Mutants of Saccharomyces cerevisiae

To show the occurrence of cytochrome c 1 in ϱ − petite mutants of Saccharomyces cerevisiae , in which its presence was questioned, low‐temperature absorption spectra of various ϱ + ϱ − strains have been compared. Some of these strains carry nuclear mutations producing different types of cytochrome deficiencies, thus lowering the spectral interferences on cytochrome c 1 and making easier its observation. The comparison was made with whole cells and with mitochondrial preparations. All the ϱ − mutants examined present a shoulder or a peak at a wavelength corresponding to cytochrome c 1 in the ϱ + strains. This absorption band at 552 nm in ϱ − mutants was further identified by isolating a cytochrome with an α absorption maximum at this wavelength. The low‐temperature absorption spectrum of this cytochrome was compared to low‐temperature absorption spectra of cytochrome c 1 isolated from a wild‐type strain, and of cytochrome c and cytochrome b 2 . It is similar, if not identical, to the spectrum of the wild‐type cytochrome c 1 , and quite distinct of that of the other cytochromes. The cytochrome c 1 content, in the various ϱ + and ϱ − strains examined, is estimated with the help of a calculation procedure taking into account the spectral cross interferences of the cytochromes. In the absorption spectra of the ϱ − strains, a shoulder is recorded at about 557–558.5 nm. The nature of this shoulder is discussed.