The respiratory system of Rhodotorula glutinis. II. Mechanism of inhibitor tolerant respiration.

The mechanism of inhibitor-tolerant respiration in Rhodotorula glutinis was studied. This inhibitor-tolerant respiratory pathway was not due to the presence of an excess of cytochrome c oxidase, nor to the operation of an inhibitor-resistant cytochrome c oxidase. Carotenoids do not appear to be involved in this respiratory chain pathway; data are also presented which show that the inhibitors penetrate into the cell. Although the initial rate of oxygen uptake by intact cells was not inhibited in the presence of cyanide or antimycin A, in the presence of these inhibitors the rate of oxygen uptake decreased significantly when the oxygen concentration fell below 100 mum. This change in rate of oxygen uptake as a function of pO(2), suggests that a respiratory chain with a low affinity for oxygen operates in the presence of inhibitors. The characteristics of this alternate pathway are described.