Glucosyltransferase Activities in Liver Mitochondria

Mitochondria, and specially outer mitochondrial membranes, incorporate d ‐[ 125 C]glucose from UDP‐ d ‐[ 14 C]glucose into products extracted with organic solvents and into a residual precipitate, with a pH optimum of about 6.5 in (2‐ N ‐morpholine‐ethane)‐sulfonic acid (MES) buffer. The chloroform/methanol (2:1, v/v) extract contains two products. The major [ 14 C]glucolipid is stable to mild alkali, but releases [ 14 C]glucose upon mild acid hydrolysis. It is retained on DEAE‐cellulose (acetate form) and is eluted with the same ionic strength as an hexosyldolichyl monophosphate diester. This [ 14 C] glucolipid has the same chromatographic behaviour as dolichyl‐mannosylphosphate in neutral, acidic and basic solvent systems; and its biosynthesis is greatly increased by exogenous dolichylmonophosphate. the other [ 14 C]glucolipid is stable upon mild acid hydrolysis and is not retained on DEAE‐cellulose. On silicic acid it is eluted with acetone. The biosynthesis of this compound is stimulated by exogenous ceramide. This glucolipid has the same chromatographic mobility in different solvent systems as glucosylceramide isolated from the liver of a patient with Gaucher's disease. Biosynthesis of these two glucolipids is inhibited by UDP, but only biosynthesis of dolichylglucosyl monophosphate is reversible with this nucleotide. The biosynthesis of these different glucosylated derivatives is stimulated by the addition of divalent cations (Mn 2+ , Mg 2+ ). The effect of these two metal ions on dolichylglucosyl monophosphate and glucosylceramide formation is studied in different conditions.