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Papers In Press, published online ahead of print January 11, 2002
Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA 90095-1569
Corresponding Author: cathy{at}mbi.ucla.edu
Coenzyme Q (Q) is an essential component of the mitochondrial respiratory chain in eukaryotic cells, and is present in other cellular membranes where it acts as an antioxidant. Since Q biosynthesis in Saccharomyces cerevisiae occurs within mitochondria, the intracellular distribution of Q indicates the existence of intracellular Q transport. In this study, the uptake of exogenous Q6 by yeast and its transport from the plasma membrane to mitochondria was assessed in both wild-type and in Q-less coq7 mutants derived from four distinct laboratory yeast strains. Q6 supplementation of media containing ethanol, a nonfermentable carbon source, rescued growth in only two of the four coq7 mutant strains. Following culture in media containing dextrose, the added Q6 was detected in the plasma membrane of each of four coq7 mutants tested, indicating that each of the four coq7 mutant strains assimilate exogenous Q6 into the plasma membrane. The two coq7 mutant strains rescued by Q6 supplementation for growth on ethanol contained mitochondrial Q6 levels similar to wild-type. However, the content of Q6 in mitochondria from the non-rescued strains was only 35% and 8% respectively, of that present in the corresponding wild-type parental strains. In yeast strains rescued by exogenous Q6, succinate-cytochrome c reductase activity was partially restored, whereas non-rescued strains contained very low levels of activity. There was a strong correlation between mitochondrial Q6 content, succinate cytochrome c reductase activity and steady state levels of the cytochrome c1 polypeptide. These studies show that transport of extracellular Q6 to the mitochondria operates in yeast, but is strain dependent. When Q biosynthesis is disrupted in yeast strains with defects in the intracellular transport of exogenous Q, the bc1 complex is unstable. These results indicate that delivery of exogenous Q6 to mitochondria is required for activity and stability of the bc1 complex in yeast coq mutants.
J. Biol. Chem, 10.1074/jbc.M112222200
Submitted on December 20, 2001
Revised on January 11, 2002
Accepted on January 11, 2002
Uptake of exogenous coenzyme Q and transport to mitochondria is required for bc1 complex stability in yeast coq mutants
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