Abstract
The formation of cytochrome c oxidase in yeast is dependent on oxygen. In order to examine the oxygen-dependent formation of the active enzyme, the effect of oxygen on the synthesis and the assembly of cytochrome c oxidase subunits was studied. Pulse-labeling experiments revealed that oxygen has no significant immediate effect on the synthesis of the three mitochondrially made subunits I to III; however, its presence causes subunits I and II to form a complex with the cytoplasmically made subunits VI and VII. This "assembly-inducing" effect can be demonstrated with intact yeast cells as well as with isolated mitochondria. It is independent of cytoplasmic or mitochondrial protein synthesis. After anaerobic growth for 10 or more generations, the intracellular concentrations of individual cytochrome c oxidase subunits drop 10- to 100-fold. Most of these residual subunits are not assembled within a functional cytochrome c oxidase molecule.
Highlights
After anaerobic growth for 10 or more generations, the intracellular concentrations of individual cytochrome c oxidase subunits drop lo- to loo-fold
Presence of Cytochrome c Oxidase Subunits in Anaerobically Grown Yeast Cells--The
A-decorated immune replica technique permits the identification and quantitation of individual polypeptides in total ceil homogenates and subcellular fractions [13]. This method was used to measure the levels of cytochrome c oxidase subunits II, IV, V, VI, and VII in wild type yeast cells after either aerobic or anaerobic growth
Summary
After anaerobic growth for 10 or more generations, the intracellular concentrations of individual cytochrome c oxidase subunits drop lo- to loo-fold. Earlier studies [7] had suggested that pulse-labeling of cytochrome c oxidase subunits I and II in intact yeast cells was dependent on oxygen whereas labeling of the other subunits of the enzyme was relatively oxygen independent. This observation was later extended to pulse-labeled isolated mitochondria [10]. In some of these pulse-labeling studies, the labeled cytochrome c oxidase subunits were only detected after immunoprecipitation from mitochondrial extracts that had been enriched in cytochrome c oxidase by ammonium sulfate fractionation.
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