title: Biosyntheses of galactosyl lipids and polysaccharide in Streptococcus mutans.
abstract: The syntheses of galactosylphospholipids and a galactose-containing polymer were observed when radio-labeled UDP-galactose was incubated with the membrane enzymes prepared from a strain of Streptococcus mutans, FA-1. The lipids were resolved into two components, lipids-1 and -2, by thin-layer and DEAE-cellulose column chromatographies. In the latter chromatography, lipid-1 was eluted by 0.0075 M and lipid-2 by 0.18 M ammonium acetate. The syntheses of lipids-1 and -2 were strongly inhibited by UDP and UMP, respectively. Both lipids-1 and -2 were degraded by mild acid, but were stable to mild alkaline hydrolysis. These results, together with their mobilities on thin-layer chromatography, suggest that lipid-1 is a galactosylphosphorylundecaprenol, and lipid-2 is a galactosylpyrophosphorylundecaprenol. When UDP-galactose was incubated with radiolabeled undecaprenol and ATP in the presence of membrane enzymes, lipids with thin-layer chromatographic mobilities of lipid-1 and lipid-2 were observed. The phosphate-to-galactose ratios in lipid-1 and lipid-2 were determined to be 1:1 and 2:1, respectively. These results indicated that lipid-1 and lipid-2 formed are galactosylmonophosphorylundecaprenol and galactosylpyrophosphorylundecaprenol, respectively. The polymer formed was eluted from the DEAE-cellulose column with a low concentration of salts (less than 0.1 M), suggesting that it is probably a polysaccharide, but not a lipoteichoic acid or teichoic acid-type polymer. In order to identify the sugars present in the polymer synthesized, the polymer purified by Sephadex G-50 and DEAE-cellulose column chromatographies was subjected to acid hydrolysis followed by NaB3H4 reduction and paper chromatographic analysis. [3H]Galactitol and a small amount of [3H]galactosaminitol were detected. This result suggests that the polymer is a nascent polysaccharide containing mainly galactose and a small amount of galactosamine, which probably derived from N-acetylgalactosamine during acid hydrolysis of the polymer.
authors.affiliation: Department of Microbiology and Biochemistry, University of Pittsburgh, School of Dental Medicine, PA 15261.
authors.forename: T H
authors.initials: TH
authors.lastname: Chiu
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D038983:Galactolipids; D006017:Glycolipids / Q000096:biosynthesis*; D008563:Membrane Lipids / Q000096:biosynthesis*; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D013295:Streptococcus mutans / Q000378:metabolism*; D014531:Uridine Diphosphate Galactose / Q000378:metabolism
chemical_list: D038983:Galactolipids; D006017:Glycolipids; D008563:Membrane Lipids; D011135:Polysaccharides, Bacterial; D014531:Uridine Diphosphate Galactose