The effect of excess mevalonic acid on ubiquinone and tetrahymanol biosynthesis in Tetrahymena pyriformis.

When T. pyriformis is grown in the presence of 10(-2)M-mevalonic acid, the uptake exceeds the cell's requirement for this biosynthetic intermediate. The majority of the excess mevalonic acid is diverted into ubiquinone-8 biosynthesis whereas the biosynthesis of tetrahymanol, the major product of the mevalonic acid pathway, is unchanged. In the presence of excess external mevalonic acid, the biosynthesis of mevalonic acid by the cell is inhibited. It is proposed that ubiquinone biosynthesis is normally regulated by mevalonic acid availability, whereas tetrahymanol biosynthesis is regulated primarily at a later point in the pathway.