Abstract
1. Conditions have been established for the sulphate-limited growth of Torulopsis utilis in continuous culture. 2. Mitochondria prepared from sulphate-limited cells lack both piericidin A sensitivity and the first energy-conservation site (site 1). Sensitivity to antimycin A or cyanide and the second and third energy-conservation sites were apparently unaffected by sulphate-limited growth. 3. Aerobic incubation for 8h of sulphate-limited cells with a low concentration of sulphate (50mum or less) resulted in the recovery of mitochondrial piericidin A sensitivity and site 1. The use of higher concentrations of sulphate (250mum or more) still resulted in the recovery of mitochondrial piericidin A sensitivity and site 1, but also resulted in the appearance of a non-phosphorylating oxidase, which mediated oxidation of the respiratory chain at about the level of cytochrome b in an antimycin A- and cyanide-insensitive manner. Both this alternative route and the conventional normal route of respiration were shown to coexist and to intercommunicate at the level of cytochrome b. 4. Low-temperature spectroscopy failed to identify any new respiratory component to explain the alternative route. 5. The apparent affinity of the alternative route for oxygen was similar to that for the conventional route through cytochrome oxidase, namely half-maximal activity at 0.1mum-oxygen or less. 6. The non-haem iron concentration of submitochondrial particles was unaffected by sulphate limitation, whereas the acid-labile sulphide concentration was lowered tenfold. Marked increases (between four- and 30-fold) in the acid-labile sulphide concentration of submitochondrial particles were observed in sulphate-limited cells after aerobic incubation with various concentrations of sulphate. The lowest increase (fourfold) was observed without added sulphate, the highest (30-fold) with 1.0mm added sulphate. 7. The ratio of non-haem iron to acid-labile sulphide in submitochondrial particles varied with different growth conditions from a maximum of 15.0 to a minimum of 0.72. It is suggested that analytical measurements of non-haem iron are an inadequate guide to the concentration of iron-sulphur protein in complex systems. 8. The effects of sulphate-limited growth on site 1 and piericidin sensitivity are interpreted to indicate a role for iron-sulphur protein in these properties. 9. The aerobic incubation of sulphate-limited cells with cycloheximide resulted in the recovery by mitochondria of site 1 but not of piericidin sensitivity. 10. The appearance of the alternative route for cyanide- and antimycin-A (but not piericidin A-) insensitive respiration on incubating sulphate-limited cells with sulphate concentrations higher than 250mum indicates that the alternative route involves an iron-sulphur protein.