Identification of the lipid intermediate in yeast mannan biosynthesis.

Abstract

The unsaponifiable lipid fraction of Saccharomyces cerevisiae contains a phosphorylated component which accepts a mannosyl residue from GDP‐mannose and transfers it to growing mannan chains. Both reactions are catalyzed by membrane‐bound enzymes. The lipid component has been purified more than 1000‐fold (based on lipid‐bound phosphate). After dephosphorylation with an orthophosphoric monoester phosphohydrolase this acceptor was shown by mass spectroscopy to be identical with authentic yeast dolichol. The “lipid” intermediate in yeast cell wall biosynthesis, therefore, is mannosylated dolichol. The “lipid” intermediate intermediate in yeast cell wall biosynthesis, therefore, is mannosylated dolichol monophosphate.Yeast dolichol is a mixture of five homologous polyprenols with saturated α‐isoprene units, as shown by Dunphy et al. in 1967. All these homologues seem also to be present in the cells as monophosphates. As compared to free dolichols the phosphorylated forms only amount to about 10–20%.