MEVALONATE-DERIVED ISOPENTENYL DIPHOSPHATE IS THE BIOSYNTHETIC PRECURSOR OF UBIQUINONE PRENYL SIDE-CHAIN IN TOBACCO BY-2 CELLS

Study of the incorporation of C-13-labelled glucose or pyruvate into t he isoprenoids of tobacco BY-2 cells allowed the biosynthetic origin o f isopentenyl diphosphate to be determined. Sterols synthesized in the cytoplasm and the prenyl chain of ubiquinone Q10 located in mitochond ria were derived from the same isopentenyl diphosphate pool, synthesiz ed from acetyl-CoA through mevalonate, whereas the prenyl chain of pla stoquinone was obtained from the mevalonate-independent glyceraldehyde 3-phosphate/pyruvate route, like all chloroplast isoprenoids from hig her plants. These results are in accord with the compartmentation and complete enzymic independence of the biosynthesis of long-chain all-tr ans polyprenols in mitochondria and chloroplasts.