title: A novel glycosylphosphatidylinositol in African trypanosomes. A possible catabolic intermediate.
abstract: The major glycosylphosphatidylinositols (GPIs) in African trypanosomes are glycolipid A, the precursor of the variant surface glycoprotein membrane anchor, and glycolipid C, a species identical to glycolipid A except that it contains an acylated inositol. Both glycolipids A and C contain dimyristoyl glycerol and are efficiently labeled with [3H]myristate in a cell-free system. We now report a novel GPI known as lipid X. This GPI is radiolabeled strongly with [3H]palmitate (and very poorly with [3H]myristate or [3H]stearate) in digitonin-permeabilized cells. The structure of lipid X is Man1GlcNAc-(2O-palmitoyl)-D-myo-inositol-1-HPO4-3(lyso-pa lmitoylglyce rol). Metabolically, lipid X exists as an intermediate, and can be detected only under conditions in which its formation is stimulated (e.g. by EDTA) or its breakdown is inhibited (e.g. by Co2+). Lipid X has not been observed previously because these conditions do not support GPI biosynthesis. We speculate that lipid X is an intermediate in the catabolism of conventional trypanosome GPIs, possibly deriving from breakdown of glycolipid C.
authors.affiliation: Department of Biochemistry, Wellcome Trust Building, University of Dundee, Dundee DD1 5EH, Scotland. kgmilne@bad.dundee.ac.uk
authors.forename: K G
authors.initials: KG
authors.lastname: Milne
authors.forename: M A
authors.initials: MA
authors.lastname: Ferguson
authors.forename: P T
authors.initials: PT
authors.lastname: Englund
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism; D000818:Animals; D002240:Carbohydrate Sequence; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D004072:Digitonin / Q000494:pharmacology; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009608:Nitrous Acid; D010171:Palmitoyl Coenzyme A / Q000378:metabolism; D010739:Phospholipase D / Q000378:metabolism; D014346:Trypanosoma brucei brucei / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism
chemical_list: D000214:Acyl Coenzyme A; D010171:Palmitoyl Coenzyme A; C040349:S-tetradecanoyl-coenzyme A; C017725:stearoyl-coenzyme A; D010739:Phospholipase D; C065017:glycoprotein phospholipase D; D004072:Digitonin; D009608:Nitrous Acid