title: Thermotropic characterization of the 2-O-acyl,polyprenyl alpha-D-glucopyranoside isolated from palmitate-enriched Acholeplasma laidlawii B membranes.
abstract: The thermotropic phase behavior of a monoacylated neutral glucolipid (2-O-acyl,polyprenyl alpha-D-glucopyranoside), isolated from palmitate-enriched Acholeplasma laidlawii B membranes, was studied by differential scanning calorimetry, infrared spectroscopy and X-ray diffraction. When equilibrated at low temperatures, aqueous dispersions of this lipid form an ordered, crystal-like lamellar gel phase which transforms to an inverted hexagonal phase at temperatures near 65 degrees C upon heating. However, upon cooling from high temperatures, the inverted hexagonal phase remains stable down to temperatures near 45 degrees C. Further cooling first results in the formation of a metastable lamellar liquid crystalline phase at temperatures near 35 degrees C and then a metastable gel phase at lower temperatures. The metastable gel phase, if immediately reheated at a fast scan rate, undergoes a gel/liquid-crystalline phase transition at temperatures near 33 degrees C. These results indicate that this monoacylated glucolipid exhibits its gel/liquid-crystalline phase transition and its lamellar/non-lamellar phase transition at considerably lower temperatures than does the monoglycosyldiacylglycerol formed under the same conditions. When cultured in media enriched in 'high-melting' fatty acids, Acholeplasma laidlawii B synthesizes large quantities of the 2-O-acyl,polyprenyl alpha-D-glucopyranoside (up to 60 mol%) mainly at the expense of the monoglucosyldiacylglycerol (the only other nonbilayer-forming liquid normally found in the cell membrane of this organism). We thus suggest that the biosynthesis of this novel glucolipid, in response to the biosynthetic incorporation of high-melting exogenous fatty acids, is an adaptive response designed to maintain a predominantly liquid-crystalline membrane lipid bilayer at the growth temperature, while retaining the high proportion of nonbilayer-forming glucolipid species characteristic of A. laidlawii B cells cultured under these conditions.
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, Canada.
authors.forename: R N
authors.initials: RN
authors.lastname: Lewis
authors.forename: A W
authors.initials: AW
authors.lastname: Yue
authors.forename: R N
authors.initials: RN
authors.lastname: McElhaney
authors.forename: D C
authors.initials: DC
authors.lastname: Turner
authors.forename: S M
authors.initials: SM
authors.lastname: Gruner
mesh_terms: D000128:Acholeplasma laidlawii / Q000032:analysis*; D002152:Calorimetry, Differential Scanning; D002462:Cell Membrane / Q000032:analysis*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D005227:Fatty Acids / Q000378:metabolism; D006017:Glycolipids / Q000096:biosynthesis / Q000302:isolation & purification; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000032:analysis*; D013055:Spectrophotometry, Infrared; D013696:Temperature; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D005227:Fatty Acids; D006017:Glycolipids; D010169:Palmitic Acids; D019308:Palmitic Acid