Enzymatic formation of dehydrodolichal and dolichal, new products related to yeast dolichol biosynthesis

Two new polyprenyl products in addition to dehydrodolichol and dolichol were detected by two-plate silica gel thin layer chromatography of nonpolar products formed from [1-¹⁴C]isopentenyl diphosphate and farnesyl diphosphate in the reaction with a crude 1,000 x g supernatant of yeast homogenates in the presence of NADPH. The new products were indistinguishable from authentic dehydrodolichal and dolichal. Analyses of the time-dependent and pH-dependent formation of the four products including dehydrodolichal and dolichal suggested that the biosynthetic pathway from dehydrodolichol leading to dolichal is different from that to dolichol. In double-labeled experiments with a combination of [1-¹⁴C]isopentenyl diphosphate and a [4B-³H]NADPH-generating system, the ratio of ³H- and ¹⁴C-derived radioactivities found in dolichal was six times higher than that in dolichol. A small amount of all-labeled dehydrodolichol was also detected. Considering the fact that dolichol is synthesized from dehydrodolichol (Sagami, H., Kurisaki, A., and Ogura, K. (1993) J. Biol. Chem. 268, 10109-10113), we propose that dehydrodolichol is a common branch point intermediate in the biosynthetic pathways leading to dolichal and dolichol and that dehydrodolichal is an intermediate in the pathway from dehydrodolichol to dolichal.