Hauksson JB, Lindblom G, Rilfors L Structures of glucolipids from the membrane of Acholeplasma laidlawii strain A-EF22. II. Monoacylmonoglucosyldiacylglycerol Biochimica et Biophysica Acta1215 (1994)
341-345
NCBI PubMed ID:7811721 Publication DOI:10.1016/0005-2760(94)90063-9 Journal NLM ID:0217513 Publisher: Elsevier Institutions: Department of Physical Chemistry, Umeå University, Sweden
The structure of one glucolipid from the membrane of Acholeplasma laidlawii, strain A-EF22, was determined. This glucolipid is synthesized only when a large fraction of saturated, straight-chain fatty acids are incorporated into the membrane lipids of strain A-EF22. The lipid was studied by 1H- and 13C-NMR spectroscopy. The structure of the lipid is 1,2-diacyl-3-O-[6-O-acyl-(α-D-glucopyranosyl)]-sn-glycerol. The result for this lipid shows that a previously published structure, based on incomplete chemical analyses, was incorrect. The phase equilibria for 1,2-diacyl-3-O-[6-O-acyl-(α-D-glucopyranosyl)]- sn-glycerol and the two dominating lipids in A. laidlawii, monoglucosyldiacylglycerol and diglucosyldiacylglycerol, are discussed and related to the chemical structure of the lipids.
Related record ID(s): 109545, 109546 NCBI Taxonomy refs (TaxIDs):2148 Reference(s) to other database(s): CCSD:45269, CBank-STR:762 Show glycosyltransferases
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Rawyler A, Meylan-Bettex M, Siegenthaler PA (Galacto)lipid export from envelope to thylakoid membranes in intact chloroplasts. II. A general process with a key role for the envelope in the establishment of lipid asymmetry in thylakoid membranes Biochimica et Biophysica Acta1233 (1995)
123-133
Taxonomic group: plant / Streptophyta (Phylum: Streptophyta) Organ / tissue:leaf
NCBI PubMed ID:7865537 Publication DOI:10.1016/0005-2736(94)00248-N Journal NLM ID:0217513 Publisher: Elsevier Institutions: Laboratoire de Physiologie Végétale, Université de Neuchâtel, Switzerland
The transfer of organelle of newly synthesized lipid molecules from inner envelope to thylakoid membranes, as well as their subsequent transbilayer distribution in these membranes, have been studied in intact chloroplasts isolated from young and mature spinach, young pea and mature lettuce leaves, using a recently developed methodology (Rawyler, A., Meylan, M. and Siegenthaler, P.A. (1992) Biochim. Biophys. Acta 1104, 331-341). Three radiolabelled precursors were used. UDP-[14C]galactose allowed to follow the fate of mono- and digalactosyldiacylglycerol (MGDG and DGDG) made from polyunsaturated, preexisting diacylglycerol (DAG), whereas [14C]acetate and [14C]glycerol 3-phosphate were used to follow the fate of MGDG and phosphatidylglycerol (PG), respectively, after de novo synthesis. MGDG, DGDG and PG molecules assembled at the envelope level were found to be exportable to thylakoids in amounts strictly proportional to the amounts synthesized, provided that the necessary substrates were not limiting. Lipid export was class-selective; under our conditions, as much as 50-80% of the MGDG, 87% of the PG and 20-30% of the DGDG synthesized were exported to thylakoids. However, within the MGDG class labelled from [14C]acetate, there was hardly any selectivity in the export of its various molecular species. For MGDG, the proportionality coefficient, which reflects the efficiency of the export process, was higher in chloroplasts from young than from mature leaves, and higher in spinach than in pea and lettuce. Temperature affected the efficiency of galactolipid export in a class-dependent way. MGDG synthesis and export had similar Q10 values of about 4 in young and 3 in mature spinach leaves, while the Q10 of DGDG export was higher than that of its synthesis. In most cases, the transmembrane distribution of labelled lipids in thylakoids was found to match closely the corresponding distribution of mass, regardless of plant age and species and of incubation time and temperature. In some cases however, small but significant differences occurred between the label and the mass transbilayer distributions of MGDG (labelled molecules more inwardly oriented), DGDG and PG (more outwardly oriented). We propose a general model in which the thylakoid lipid asymmetry is primarily preestablished in the chloroplast envelope by the topography of its lipid-synthesizing enzymes, together with the occurrence of relatively fast lateral diffusion and translocation rates of the newly synthesized lipids. Transient fusions between inner envelope and thylakoid membranes would allow lipid export by lateral diffusion and build the observed lipid asymmetry in the latter.
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