Disaccharide units

FIGURE 25 11 Diagram of a cell surface glycoprotein showing the disaccharide unit that IS recognized by an invading influenza virus... 

Hyaluronic acid consists of an unbranched chain of repeating disaccharide units containing GlcUA and GlcNAc. Hyaluronic acid is present in bacteria and is widely distributed among various animals and tissues, including synovial fluid, the vitreous body of the eye, cartilage, and loose connective tissues. 

GlcUA but with GalNAc replacing GlcNAc. The GalNAc is substituted with sulfate at either its 4 or its 6 position, with approximately one sulfate being present per disaccharide unit. 

As shown in Figure 48-8, the keratan sulfates consist of repeating Gal-GlcNAc disaccharide units containing sulfate attached to the 6 position of GlcNAc or occasionally of Gal. Type 1 is abundant in cornea, and type II is found along with chondroitin sulfate attached to hyaluronic acid in loose connective tissue. Types I and II have different attachments to protein (Figure 48—8). 

Figure 48-9. Structure of heparin. The polymer section illustrates structural features typical of heparin however, the sequence of variously substituted repeating disaccharide units has been arbitrarily selected. In addition, non-O-sulfated or 3-0-sulfated glucosamine residues may also occur. (Modified, redrawn, and reproduced, with permission, from Lindahl U et al Structure and biosynthesis of heparin-like polysaccharides. Fed Proc 1977 36 19.)...

The conformational analysis was developped recently by different authors first on the disaccharide units to investigate the role of the charge on C-6 position on the conformation [29-32]. From this study, the 2i or right-handed 3i helices were described as most problable conformations [30,31]. These conformations were also demonstrated from x-ray diffraction [33] or on the basis of circular dichroTsm [34], From these data, the repeat unit in the axial-axial conformation has a 4.3 A° length which will be used to characterize the electrostatic properties. 

Carbohydrates are the most abundant, weight-wise, organic material available. Photosynthesis produces about 400 billion tons annually. The polysaccharides are generally composed of mono- and disaccharide units. 

BL = beef lung SM = sheep-intestinal mucosa PD = pig duodenum PM = pig-intestinal mucosa. 8 Residues per disaccharide unit.c Lipoproteinlipase-inducing units. Fractions from PM I. 

D-Clucuronic acid residues in heparin are linked as in disaccharide units 1 and 2, that is, either to 2-acetamido-2-deoxy-D-glucose ( Ana) or to 2-deoxy-2-sulfoamino (ANS) residues. (Although not apparent from Scheme 1, the amino sugar can be sulfated at C-6.)... 

Fic. 6.—Proposed Distribution of Disaccharide Units Along an Average Heparin Chain.151 [For simplicity, possible linkage regions and antithrombin-binding sequences are not considered. For notations, see legend and footnote to Scheme 1. Arrows indicate possible insertion of units G-Ana.]... 

The non-reducing disaccharide unit of raffinose and gentianose is certainly sucrose, as previously mentioned in the case of melezitose all that can be said with assurance at the present time is that this sugar is 8-[a-T>-glucopyrano8yl2-(f)-T>-fructofuranosyl-a-j)-glucopyranoside. It would indeed be surprising, from biological views, if the now unknown disaccharide component should eventually prove to be other than sucrose,... 

The repeat distance is 28.5 A (2.85 nm). The molecule is a helix having three disaccharide units with a projected height of 9.5 A (950 pm). 

Andersson, B., Dahmen, J., Freid, R., Leffler, H., Magnusson, G., Noori, G., and Svanborg-Evan, C. (1983). Identification of an active disaccharide unit of glycoconjugate receptor for pneumococci attaching to human pharyngeal epithelial cells. /. Exp. Med. 158,559-570. 

Vancomycin aglycone (VAG) contains the same peptide scaffold as vancomycin, but it lacks the disaccharide unit (C53H52CI2N8O17, molecular mass of 1142). The basic... 

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