Glycoproteins oligosaccharides from blood

Selectins are a family of plasma membrane lectins that mediate cell-cell recognition and adhesion in a wide range of cellular processes. One such process is the movement of immune cells (T lymphocytes) through the capillary wall, from blood to tissues, at sites of infection or inflammation (Fig. 7-33). At an infection site, P-selectin on the surface of capillary endothelial cells interacts with a specific oligosaccharide of the glycoproteins of circu-... 

Figure 47-2. Structures of two 0-linked oligosaccharides found in (A) submaxillary mucins and (B) fe-tuin and in the sialoglycoprotein of the membrane of human red blood cells. (Modified and reproduced, with permission, from LennarzWJ The Biochemistry of Glycoproteins and Proteoglycans. Plenum Press, 1980.)...

A similar mechanism is apparently responsible for removing old erythrocytes from the mammalian bloodstream. Newly synthesized erythrocytes have several membrane glycoproteins with oligosaccharide chains that end in NeuSAc. When the sialic acid residues are removed by withdrawing a sample of blood, treating it with sialidase in vitro, and reintroducing it into the circulation, the treated erythrocytes disappear from the bloodstream within a few hours those with intact oligosaccharides (erythrocytes withdrawn and reintroduced without sialidase treatment) continue to circulate for days. 

Ten sialic-acid-containing oligosaccharides and four neutral oligosaccharides have been purified from the major glycoprotein fraction of hog, submaxillary-gland mucin. H-N.m.r. spectroscopy at 360 MHz, in combination with methylation analysis and mass spectrometry, allowed the determination of their structures, which are partial structures of a pentasaccharide (see Fig. 42) having blood-group A activity.221... 

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