Possible involvement of 3-hydroxymethylglutaryl-CoA reductase in determining the side-chain length of ubiquinone in rat heart.

The biosynthetic mechanism for determining the side-chain length of ubiquinone in rat heart mitochondria was investigated. The biosynthesis of nonaprenyl ubiquinone (UQ-9) and decaprenyl ubiquinone (UQ-10) in the mitochondria from rat hearts previously perfused with mevalonolactone was accelerated depending on the concentration of mevalonolactone. Furthermore the synthesis ratio between UQ-10 and UQ-9 (UQ-10/UQ-9) increased in accordance with the increasing concentration of mevalonolactone used. In addition, an enhancement of the synthesis ratio (UQ-10/UQ-9) was observed when the rats were treated with isoproterenol to increase the activity of 3-hydroxymethylglutaryl-CoA (HMG-CoA) reductase, a rate-limiting enzyme which forms mevalonate. Moreover, the addition of isopentenyl pyrophosphate, which is a metabolite of mevalonate, elevated the synthetic ratios UQ-10/UQ-9 in intact mitochondria and decaprenyl pyrophosphate/solanesyl pyrophosphate in the partially purified polyprenyl pyrophosphate synthetase from rat heart. These results suggest that the HMG-CoA reductase could be involved as a determining factor of the side-chain length of ubiquinone in rat heart.