Results-Protons-Subunits-Gas-Phase-u

Dissociation of B5(14+) x S proceeds exclusively by the loss of one subunit, although the ligand increases the stability of the complex and also reduces the degree of charge enrichment in the ejected monomer. For B5(12+)(Pk)1-3, the loss of neutral Pk competes with loss of a subunit at low temperatures. Linear Arrhenius plots were obtained from the temperature-dependent dissociation rate constants measured for the loss of B from B5n+ and B514+ x S. The magnitude of the Arrhenius parameters is highly dependent on the charge state of the pentamer Ea = 35 kcalmol and A = 119 s(-1) (+14), 46 kcalmol and 123 S(-1) (+13), kcalmol and 26 s(-1) (+12), and kcalmol and (39) (+11). The Ea and A for B5(14+) x S are 59 kcalmol and () s(-1), respectively. The reaction pathways leading to greater charge enrichment of the subunit lost from the B5(14+) and B5(13+) ions correspond to higher energy processes, however, these pathways are kinetically preferred at higher temperatures due to their large A factors.

A simple electrostatic model, whereby charge enrichment leads to Coulombic repulsion-induced denaturation of the subunits and disruption of the intersubunit interactions, provides an explanation for the magnitude of the Arrhenius parameters and the origin of the asymmetric dissociation behavior of Enzymatic transglycosylation of xylose using a glycosynthase.The application of the hyperactive glycosynthase derived from Agrobacterium sp. beta-glucosidase (AbgE358G-2F6) to the synthesis of xylo-oligosaccharides by using alpha-D-xylopyranosyl fluoride as donor represents the first successful use of glycosynthase technology for xylosyl transfer. Transfer to p-nitrophenyl beta-D-glucopyranoside yields di- and trisaccharide products with beta-(1--4) linkages in 63% and 35% yields, respectively. By contrast, transfer to p-nitrophenyl beta-D-xylopyranoside yielded the beta-(1--3) linked disaccharide and beta-D-Xyl-(1--4)-beta-D-Xyl-(1--3)-beta-D-Xyl-pNP as major products in 42% and % yields, respectively. Transfer of xylose to beta-D-Xyl-(1--4)-beta-D-Xyl-pNP yielded the beta-(1--4) linked trisaccharide in 98% yield, thereby indicating that transfers to xylo-disaccharides occur with formation of beta-(1--4) bonds. human milk oligosaccharides of carbamate-protected deoxyxylonojirimycin produced a mixture of di- and tri-'saccharide' products in Structural determination of five novel tetrasaccharides containing 3-O-sulfated D-glucuronic acid and two rare oligosaccharides containing a beta-D-glucose branch isolated from squid cartilage chondroitin sulfate E.

Kinoshita-Toyoda A(1), Yamada S, Haslam SM, Khoo KH, Sugiura M, Morris HR, Dell Oversulfated chondroitin sulfate E (CS-E) derived from squid cartilage exhibits intriguing biological activities, which appear to reflect the biological activities of mammalian CS chains containing the so-called E disaccharide unit [GlcAbeta1-3GalNAc(4,6-O-disulfate)]. Previously, we isolated novel tetra- and hexasaccharides containing a rare GlcA(3-O-sulfate) at the nonreducing end after digestion of squid cartilage CS-E with testicular hyaluronidase. In this study, squid cartilage CS-E was extensively digested with chondroitinase AC-II, which yielded five highly sulfated novel tetrasaccharides and two odd-numbered oligosaccharides (tri- and pentasaccharides) containing D-Glc. Their structures were determined by fast atom bombardment mass spectrometry and (1)H NMR spectroscopy. The results revealed an internal GlcA(3-O-sulfate) residue for all the novel tetrasaccharide sequences, which rendered the oligosaccharides resistant to the enzyme. The results suggest that GlcA(3-O-sulfate) units are not clustered but rather interspersed in the CS-E polysaccahride chains, being preferentially located in the highly sulfated sequences. The predominant structure on the nearest nonreducing side of a GlcA(3-O-sulfate) residue was GalNAc(4-O-sulfate) (%), whereas that on the reducing side was GalNAc(4,6-O-disulfate) (59%).

The structural variety in the vicinity of the GlcA(3-O-sulfate) residue might represent the substrate specificity of the unidentified chondroitin GlcA 3-O-sulfotransferase. The results also revealed a trisaccharide and a pentasaccahride sequence, both of which contained a beta-d-Glc branch at the C6 position of the constituent GalNAc residue. Approximately Oligosaccharides of all disaccharide units were substituted by Glc in the Triterpene glycosides from Antarctic sea cucumbers. 1.