FIG. 1.

Biosynthesis of membrane lipid and caldariellaquinone in Sulfolobus sp. Each dashed arrow indicates a biosynthetic route catalyzed by multiple enzymes. In Sulfolobus sp., GGPP is thought to be the common precursor of hydrophobic isoprenoid compounds such as archaeal membrane lipid and caldariellaquinone (8, 11). In the largest box, two hypothetical products from GGPP obtained from the reaction with GGR from S. acidocaldarius are shown. Phytyl diphosphate, which is the final product of plant GGR, may be utilized by archaeal prenyltransferases for the biosynthesis of the isoprenoid compounds, while phytanyl diphosphate must be a dead-end product because it cannot be a prenyl donor. 3 × IPP, three molecules of IPP.