Abstract
Coenzyme Q is a mitochondrial lipid that is essential in cellular energy metabolism. Biosynthesis of Q in yeast requires nine proteins, Coq1p‐Coq9p, and deletion of any one of the yeast COQ genes leads to the decreased steady state of several other Coq polypeptides. However, when the Coq8 polypeptide is over‐expressed in some of the yeast coq null mutants, steady state levels of Coq polypeptides were restored to near wild‐type levels. We hypothesize that over‐expression of Coq8p may stabilize the Coq polypeptides by stabilizing the catalytic complex composed of Coq3p‐Coq7p and Coq9p. Using non‐denaturing 2‐dimensional blue native gels, we found that the Coq polypeptide complex dissociated upon the deletion of one of the COQ genes, but that over‐expression of COQ8 rescued the high molecular mass Coq polypeptide complex.The function of Coq9p is still unclear. In the coq9 null yeast mutant overexpressing Coq8 (Coq8 OE), IDMQ6 accumulated when fed para‐aminobenzoic acid (pABA). We hypothesize that Coq9 is required for the deimination step from IDMQ6 to DMQ6. We generated a yeast strain with the COQ9 endogenous promoter replaced by a doxycycline‐ regulated promoter. We found that DMQ6 accumulated earlier and faster than IDMQ6 when there is a very small amount of Coq9p present. The results suggest that the deimination of IDMQ6 is faster than the turnover of DMQ6.
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