Biological significance of the side chain length of ubiquinone in Saccharomyces cerevisiae.

Ubiquinone (UQ), an important component of the electron transfer system, is constituted of a quinone structure and a side chain isoprenoid. The side chain length of UQ differs between microorganisms, and this difference has been used for taxonomic study. In this study, we have addressed the importance of the length of the side chain of UQ for cells, and examined the effect of chain length by producing UQs with isoprenoid chain lengths between 5 and 10 in Saccharomyces cerevisiae. To make the different UQ species, different types of prenyl diphosphate synthases were expressed in a S. cerevisiae COQ1 mutant defective for hexaprenyl diphosphate synthesis. As a result, we found that the original species of UQ (in this case UQ-6) had maximum functionality. However, we found that other species of UQ could replace UQ-6. Thus a broad spectrum of different UQ species are biologically functional in yeast cells, although cells seem to display a preference for their own particular type of UQ.