Solubilization and Characterization of Dehydrodolichyl Diphosphate Synthase from the Yeast Saccharomyces carlsbergensis

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When the membrane fraction of Saccharomyces carlsbergensis was incubated with radiolabeled isopentenyl diphosphate in the presence of farnesyl diphosphate and Mg²⁺, phosphorylated and free long-chain polyprenols were formed. The reaction was inhibited by EDTA and heavy metal cations. A series of non-ionic detergents were studied for their efficacy to solubilize the prenyltransferase. The enzyme completely lost its activity in the presence of 0.1% of Triton X-100. n-Octyl-β-(D) glucopyranoside at the concentration of 0.25-0.5% (10-15mM) was used to solubilize the prenyltransferase. Both the membranebound enzyme and the solubilizate possessed a broad pH optimum shifted to alkaline pH values. The temperature optimum of the solubilizate was somewhat lower than that of the membrane preparation, owing to the significantly lower thermostability of the solubilized enzyme in comparison with the membrane-bound one. The phosphorylated reaction products formed in the presence of the membrane preparation had the same composition as the yeast dolichol synthesized in vivo. Non-phosphorylated polyprenols were formed during the incubation with membranes but not the solubilized enzyme. The composition of the polyprenols was also coincident with that of yeast dolichol, and the individual C₈₀-homolog of the mixture was polyprenol but not dolichol as judged by adsorption HPLC. The results are discussed in relation to the terminal stages in the biosynthesis of dolichol derivatives.