Mitochondrial Biogenesis OCCURRENCE OF NON-FUNCTIONING COMPONENTS OF THE MITOCHONDRIAL RESPIRATORY CHAIN IN SACCHAROMYCES CEREVISIAE GROWN IN THE PRESENCE OF PROTEINASE INHIBITORS: EVIDENCE FOR PROTEOLYTIC CONTROL OVER ASSEMBLY OF THE RESPIRATORY CHAIN

Yeast was grown in glucoseor galactose-containing media without or with proteinase inhibitors, phenylmethanesulphonyl fluoride and pepstatin. Culture growth was practically not affected by these compounds. Yeast growth on glucose in the presence of either phenylmethanesulphonyl fluoride or pepstatin entails accumulation of cytochromes c, cl, b and aa3 to a 25-30% excess above the control by the stationary phase, while cell respiration is unaffected. During growth on galactose the maximal cytochrome content (per unit weight of biomass) is reached in the mid-exponential phase and then decreases by 30-40% towards the stationary phase, while cell respiration remains constant. Addition of phenylmethanesulphonyl fluoride or pepstatin in the mid-exponential phase blocks the decrease in cytochrome levels and has no effect on cell respiration. Mitochondrial populations isolated from stationary-phase control and phenylmethanesulphonyl fluoride-grown cells of glucose cultures display identical succinate oxidase and partial-respiratory-chain activities, despite the differences in cytochrome contents. However, the activities of individual respiratory complexes measured after maximal activation are nearly proportional to the amounts of corresponding components. The same situation holds true for mitochondrial populations from mid-exponential-phase, stationary-phase control and stationary-phase inhibitorgrown cells of galactose cultures. The findings suggest that the 'surplus' respiratorychain components do not participate in electron flow because of the lack of interaction with adjacent carriers.