The biosynthesis of cytochrome c in yeast adapting to oxygen.

Cytochrome c probably belongs in the class of adaptive enzymes, in the sense that the cellular concentration of this chromoprotein appears to respond to the demand for its function in the utilization of oxygen (3). The substrate-induced synthesis of mammalian cytochrome c may be deduced from the findings of Drabkin (2, 4, 5) in experimental hypothyroid and hyperthyroid (thyrotoxic) rats, in which decreases and increases of oxygen consumption were attended by marked parallel alterations in the quantity of the tissue pigment. A similar inference for the cytochrome c of brewers’ yeast adapting to life in an atmosphere of oxygen was drawn by Chin (6) in Keilin’s laboratory and by Ephrussi and Slonimski (7) for the .chromoprotein in bakers’ yeast grown anaerobically, then exposed to oxygen. These investigators correlated increases in the cyanide-sensitive respiratory exchange with qualitative spectroscopic changes which occurred when these yeasts in the non-proliferative state were shifted from their anaerobic environment to oxygen. Before exposure to oxygen two absorption bands were present, one at 556 to 566 rncc attributed to cytochrome b1 and a second weak band at 535 to 599 rncc ascribed to cytochrome al. The latter may be owing to the more recently described yeast hemoglobin (8). After exposure to oxygen the above spectrum was replaced by another, characteristic of cytochromes a, b, and c. Similar spectroscopic changes in anaerobic cells adapting to aerobic existence had been discovered much earlier by Tamiya (9) in AspergiZZus oryzue and by Fink (10) in brewers’ yeast, but they had been attributed by these early workers to the selective growth and multiplication of certain cells already present in the anaerobic state. Recently, it has been found that two other hemin