The development of cytochromes during the cell cycle of a glucose-repressed fission yeast, Schizosaccharomyces pombe 972h⁻

1. Spectrophotometric analysis of intact cells of Schizosaccharomyces pombe, harvested from exponentially growing cultures during the phase of glucose repression, revealed the presence of cytochromes a+a₃, c and at least two species of cytochrome b. 2. An absorption maximum at 554nm at 77°K, previously attributed to cytochrome c₁, has been identified as a b-type cytochrome. 3. CO-difference spectra reveal the presence of cytochromes P-420 and P-450 in addition to cytochrome a₃. 4. The cell cycle was analysed by separation of cells into classes representing successive stages in the cell cycle by isopycnic zonal centrifugation. 5. Cytochromes c₅₄₈, b₅₅₄ and b₅₆₀ each exhibited a single broad maximum of synthesis during the cell cycle. 6. Amounts of cytochromes a+a₃ and b₅₆₃ (tentatively identified as cytochrome b_T by its reaction on pulsing anaerobic cell suspensions with O₂) oscillated in phase, and showed two maxima during the cycle; the second maximum of cytochromes a+a₃ was coincident with a maximum of activity of enzymically active cytochrome c oxidase. 7. The amount of cytochrome P-420 decreased during the first three-quarters of the cell-cycle, whereas that of cytochrome P-450 increased during this period. 8. The discrepancy between spectrophotometric and enzymic assay of cytochrome c oxidase, the changing ratio of cytochrome a₃/cytochrome a and the relationship between changes in cellular content of cytochromes and previous observations on respiratory oscillations during the cell cycle are discussed.