New cell recognition system based on the interaction between carbohydrates of glycolipids on cell surfaces is described. Specific carbohydrate-carbohydrate interactions between some kinds of glycolipids were observed using glycolipid-containing liposomes and glycolipid coated solid phase. In addition, glycolipid dependent cell adhesion which occurs through specific carbohydrate-carbohydrate interaction was also observed. The carbohydrate-carbohydrate interactions are able to show both attractive and repulsive interactions which depend on the carbohydrate structures, whereas interactions of other cell recognition molecules such as adhesive proteins and carbohydrate binding proteins show only adhesion. The specificity and strength of carbohydrate-carbohydrate interaction are also controlled by fattyacid composition of glycolipid, and surface glycolipid density. Thus, the specificities of the cell recognition system through carbohydrate-carbohydrate interaction could vary more than those of other cell recognition systems through protein-protein and protein-carbohydrate interactions.
Endoglycoceramidase (EGCase) cleaves the linkage between oligosaccharides and ceramides of various glycosphingolipids, leaving simultaneously both intact ceramides and oligosaccharides. Taking advantage of the specificity of EGCase, we have found it very useful in the structural studies of glycosphingolipids.A detergent was required for EGCase to express full activity, possibly due to their hydrophobic nature, and therefore EGCase cannot be used for research on live cells. Recently, activator proteins regarding the stimulation of EGCase activity in the absence of detergents were discovered. When using activator proteins in place of Triton X-100 for stimulating EGCase activity, it was also noted to cause no damage to intact cells. It is thus possible by activator proteins to elucidate the biological functions of endogenous glycosphingolipids in situ by EGCase.
Glycolipids are the hybrid molecules constructed with the hydrophilic carbohydrate chain and the hydrophobic side chain. The characteristic change in the structure of glycolipids is usually observed among different animal species, different organs, tissues and cells of the same animals, and cells in the different proliferation-and differentiation-stages. Recent approaches for characterization of the meaning on the glycolipid-heterogeneity clearly indicates the involvement of glycolipids in a signal transducer and a modulator of functional proteins. For example, glycolipids appeared in association with differentiation can effectively induce the differentiation in human myeloid and monocytoid leukemia cells, and the keratinization in fetal rat keratinocytes. And addition of glycolipids, which do not contain in the target neuroblastoma cells, to the culture medium, can induce the neurite outgrowth of the cells.
Among the biologically active glycolipids, much attention is now focused on gangliosides because of their newly discovered involvement in cell growth, differentiation, adhesion, oncogenesis, and so on. Gangliosides are structurally heterogenous molecules, composed of a glycan chain containing sialic acid (s) and a hydrophobic ceramide. They are located as very minor constituents on the plasma membrane of almost all mammalian cells. In order to elucidate the structure-function relationships at the molecular level, the syntheses of a variety of gangliosides, including their derivatives and analogs, are of absolute necessity. This article describes the systematic chemical syntheses of gangliosides with a special reference to our methods. Also, some analyses of biological functions and biomedical applications are discussed.
Glycolipid-analogous polysaccharides with well-defined structures are of interest in connection with the development of new types of specialty polysaccharides. This review article highlights the following four topics. (1) Emulsan, a naturally occurring microbial surfactant polysaccharide, is an efficient emulsifier. (2) Trialkylcellulose prepared by esterification of cellulose forms Langmuir-Brodget membranes. (3) Cyclodextrins substituted with long alkyl chain in position 6 of each glucose unit are found to form monolayers, which bind guest molecules to assemble host-guest LB membranes. (4) Three types of regiospecifically modified polysaccharides were synthesized via ring-opening polymerizations of anhydro sugar derivatives. (a) 3-O-Octadecyl- (1→6) -α-D-glucopyranan homopolysaccharide, (b) Partially 3-O-octadecylated (1→6) -α-D-glucopyranans, (c) Copolysaccharides consisting of nonsubstituted and 2, 3, 4-tri-O-substituted glucose units. Their functions based on the amphiphilic properties are discussed.
Several methodologies for making liposome more stable and more cell specific are introduced in this review article. They involve reconstitutions of glycoproteins or glycolipids into liposomal membranes and coating the outermost surface of liposomal membranes with naturally occurring polysaccharides. Results in the in vitro and in vivo evaluation of such the modified liposomes are also described from the view points of their chemical, physicochemical, and biochemical stabilities and cell compatibility and specificity. In addition, the usefulness of these glyco-conjugated liposomes, for example, in receptormediated drug targeting or liposomal vaccines in medicine and serum free cell culture in biotechnology, is briefly introduced.
Poly (sodium carboxylate) s containing glucopyranose residues as biodegrading segments in the polymer chain were prepared from starch by partial conversion of the vicinal diols of glucopyranose units into the corresponding dicarboxylates via dialdehydes. Their biodegradability and building performance in detergents were examined. Relation of glucopyranose group content in the polymer chain with biodegradability as well as functionality are discussed. Polycarboxylates containing glucopyranose residues as biodegradable segments were shown to have improved biodegradability and better building performance in detergents, and thus may be useful as biodegrading units in a polymer. Some microbes capable of degrading polycarboxylates were isolated by an enrichment culture technique from activated sludge. Biodegradability and building performance in detergents of the polycarboxylates were also found to vary inversely with the degree of dicarboxylation. Polymers with a lower degree of dicarboxylation, e.g. a higher glucopyranose content, showed better biodegradability.
A new method, a combination of the tape-stripped and paper-absorbent methods, was developed for measuring the distribution of peroxide and skin surface lipids on their depth in human stratum corneum. Peroxide lipids were shown to be produced not only in the top layer of the stratum corneum in the skin of people not exposed to sunlight but in the deep layer as well. Their compositions were correlated to those of skin surface lipids. Peroxide lipids in the outer layer were more easily produced than those in inner layers, possibly due to higher squalene content in the outer lipids. The removal of peroxide and skin surface lipids from the stratum corneum was also conducted and the washing properties were noted to differ. Peroxide lipids not only in the outer layer but also in the inner layer could be washed away while washing removed skin surface lipids only from the top layer. The addition of a cleanser enhanced removal efficiency. The removal efficiency of three surfactants differing in hydrophilic groups, i.e. phosphate, sulfate and carboxylate groups, was assessed. The phosphate type surfactant was found more capable of removing skin surface lipids in the stratum corneum. Based on the present results, an ideal cleanser should wash away peroxide lipids situated deeply within and harmful to the skin, but only skin surface lipids which function as a surfactant barrier.
A specific method for determining α-mannosidase activity was developed using an enzymelinked immunosorbent assay (ELISA) and a specific polyclonal antibody which recognizes theterminal Man β1-4 structure of the reaction product, mannosylglucosylceramide (Man β1-4 Glc β1-ceramide, MlOse2Cer). In the assay, the dimannosylglucosylceramide substrate (Man α1-3 Man β1-4 Glc β1-ceramide, MlOse3Cer) immobilized on the solid phase of a 96-wellmicrotiter plate was incubated with Canavalia ensiformis α-mannosidase in citrate buffer containing detergent. The optimum conditions for the enzyme assay were as follows : buffer solution, 0.05 M citrate buffer (pH 4.04.5); detergent, sodium taurodeoxycholate (40 μg); enzyme concentration, 1.0 μg (1 mU); substrate concentration, 300 ng (300 pmole) : total reaction volume, 200 μL; incubation time, 1 h. Three sequential additions with washes between each were applied as follows : polyclonal antibody against the exposed Man β1-4 groups (anti-MlOse2Cer), peroxidase-conjugated anti-rabbit IgG antiserum against anti-MlOse2Cer, and peroxidase substrate. By this method, it became possible to quantitate the amount of reaction product, MlOse2 Cer, when present as low as 25 pmole.