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+ or 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 c1 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 c1 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 c1 isolated from a wild-type strain, and of cytochrome c and cytochrome b2. It is similar, if not identical, to the spectrum of the wild-type cytochrome c1, and quite distinct of that of the other cytochromes. The cytochrome c1 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. [ABSTRACT FROM AUTHOR]