Item – Theses Canada

OCLC number
Stewart, Robert Joseph,1960-
Surface expression of glycolipids : effect of membrane environment and glycolipid ceramide structure.
Ph. D. -- University of Toronto, 1993
Ottawa : National Library of Canada = Bibliothèque nationale du Canada, 1993.
3 microfiches.
University Microfilms order no. UMI00428415.
Includes bibliographical references.
The carbohydrate head groups of glycolipids may be involved in a wide variety of cell surface recognition phenomena. The recognition of glycolipids by specific external ligands depends on the accessibility or exposure of the carbohydrate at the membrane surface. The influence of changes in the composition of the membrane environment and the ceramide group of glycolipids on the exposure of their carbohydrate head groups at the bilayer surface has been examined in this study. The exposure was probed by galactose oxidase/sodium borotritide labelling of the terminal galactosyl residues of glycolipids. The oxidation of galactosylceramide (GalC) in phosphatidylcholine (PC) liposomes increased with increasing GalC fatty acid chain length and was reduced with increasing bilayer thickness or with hydroxylation of the GalC fatty acid. The oxidation of GalC in sphingomyelin (SM) liposomes was reduced compared to PC and changes in the GalC fatty acid chain length did not affect its oxidation in SM. These results were consistent with results on cerebroside sulfate (CBS) obtained earlier using antibody to CBS (M.Sc. Thesis). A divalent cation-mediated specific carbohydrate-carbohydrate interaction can occur between GalC and CBS, both present in high concentrations in myelin. This interaction may play a role in mediating the adhesion of the extracellular surfaces in myelin. Increases in the fatty acid chain length of either glycolipid increased the interaction. In contrast to its effects on the exposure of GalC and CBS mentioned above, hydroxylation of the fatty acid of either glycolipid increased the extent of interaction of their carbohydrate moieties. This could be due to participation of the hydroxyl group in interlamellar hydrogen bonding, chelation with the divalent cation or alteration of the conformation of the carbohydrate. Examination of the fine specificity of anti-CBS antibodies for CBS in different membrane environments revealed that the antigenic structure of CBS in PC bilayers is distinct from that in SM bilayers and this difference is recognized by separate pools of antibody present within the antiserum. These findings indicate that both the membrane environment and ceramide composition of glycolipids can significantly affect the receptor activity of the carbohydrate head groups of glycolipids.