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At least 523 records · Page 29Linked to original sources
PubMed1992

The synthesis of high-specific-activity UDP-[6-3H]galactose, UDP-N-[6-3H]acetylgalactosamine, and their corresponding monosaccharides.

Tritiated uridine-5'-diphosphogalactose (UDP-[3H]Gal) has been widely used to study oligosaccharide biosynthesis and structure. It can be synthesized either chemically or enzymatically using galactose oxidase to oxidize the hydroxyl moiety at C-6 to an aldehyde (6-aldo-UDP-Gal), which is then reduced back to the alcohol with tritiated sodium borohydride. Although the enzymatic approach is simple and efficient, there are several problems associated with it. First, incomplete oxidation to the aldehyde reduces the final specific activity. Second, if the galactose oxidase is not removed from the 6-aldo-UDP-Gal prior to reduction, the resulting UDP-[6-3H]Gal can be reoxidized to 6-aldo-UDP-[6-3H]Gal. We present evidence for the occurrence of this compound in one commercially obtained preparation of UDP-[6-3H]Gal. Finally, if an excess of 6-aldo-UDP-Gal is used for good yield, it is necessary to quench the reduction with nonradioactive borohydride, again reducing the final specific activity. We have devised a rapid, inexpensive, and efficient synthesis of UDP-[6-3H]Gal that circumvents all of these problems. Galactose oxidase is used to produce 6-aldo-UDP-Gal and the completeness of this reaction is confirmed on polyethyleneimine (PEI) cellulose TLC plates. The 6-aldo-UDP-Gal is purified on silica gel 60 TLC plates. This purified compound is then reduced with tritiated sodium borohydride, with the aldehyde present in excess. Unreacted 6-aldo-UDP-Gal is then purified away from the product UDP-[6-3H]Gal by chromatography on PEI cellulose. Radiochemically pure UDP-[6-3H]Gal with a specific activity of 10 Ci/mmol was obtained using the above scheme.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromatography, High Pressure Liquid↗
PubMed1992

Synthesis of high-affinity, hydrophobic monosaccharide derivatives and study of their interaction with concanavalin A, the pea, the lentil, and fava bean lectins.

Concanavalin A (Con A) and agglutinins from the pea (PSA), lentil (LCH), and fava bean (VFA) constitute a group of D-mannose/D-glucose binding legume lectins. In addition to their sugar binding specificity, these lectins also contain sites that bind hydrophobic ligands. The present study explores a class of nonpolar binding sites reportedly present adjacent to the carbohydrate binding site in PSA, LCH, and VFA. A series of 2-O- and 3-O-substituted nitrobenzoyl and nitrobenzyl derivatives of methyl alpha-D-glucopyranoside and methyl alpha-D-mannopyranoside were synthesized. Evaluation of their binding to Con A, PSA, LCH, and VFA was carried out by the technique of hapten inhibition of precipitation reaction. The hapten inhibition assay results reveal that the presence of a methyl or methylene group at the O-2 or O-3 position of the sugar is essential for hydrophobic interaction with PSA, LCH, and VFA. The substitution of methyl by nitrobenzyl leads to enhanced binding (1.7-16.7 times for the 2-O-substituted compounds and 7.9-40.5 times for the 3-O-substituted compounds) with the m-nitrobenzyl group contributing to maximum binding. A hydrophobic interaction is also involved between Con A and 2-O-nitrobenzyl derivatives, resulting in enhanced binding, but the corresponding 3-O-isomers bind poorly due probably to steric reasons. These results may be rationalized on the basis of the recently published X-ray data of Con A and VFA. The nitrobenzyl derivatives, after transformation to their azido analogs, have potential applications in the photoaffinity labeling of these lectins.

Chemical Phenomena↗
PubMed1979

Influence of enzymatic phospholipid cleavage on the permeability of the erythrocyte membrane. II. Protein-mediated transfer of monosaccharides and anions.

In order to investigate the influence of membrane lipids on transport via the protein domain of the erythrocyte membrane, a number of facilitated diffusion processes was studied by tracer flux techniques in whole cells after cleavage of up to 65% of the phosphatidylcholine or the sphingomyelin by phospholipase A2 from Naja naja or bee venom, or by sphingomyelinase, respectively. The mediated fluxes of L-arabinose, which is transported by the glucose carrier, and of L-lactate, which uses a specific monocarboxylate carrier, were markedly inhibited by cleavage of either phosphatidylcholine or sphingomyelin. These phospholipid dependencies are in line with earlier data on cholesterol dependencies (Deuticke, B. (1977) Rev. Physiol. Biochem. Pharmacol. 78, 1-97). They can only in part be explained by changes of membrane fluidity. More specific interactions of the degradation products with the carrier proteins seem also to play a role. Sulfate and oxalate transfer, which proceed via the inorganic anion-exchange system, are essentially unaffected by cleavage of phosphatidylcholine and less sensitive to sphingomyelin cleavage than the two other processes. This also agrees with earlier data on cholesterol independency of sulfate transfer. The inorganic anion-exchange protein thus seems to be less dependent on the surrounding lipids in its conformation and its mode of action than the two other carriers.

Anions↗