Structural analysis of hexa- to octa-saccharide fractions isolated from sheep gastric-glycoproteins having blood-group I and i activities

Structural data are presented on six oligosaccharide-fractions (hexa- to octa-saccharides) released from sheep -gastric-glycoproteins having blood-group I and i activity by degradation with alkaline borohydride. Previous data on two of the oligosaccharides are included for comparison. The fractions were analysed, before and after treatment with exo-β- -glycosidases and an endo-β- -galactosidase, on Bio-Gel P4 and by p.c., by direct-insertion m.s. (after methylation), and by g.l.c.—m.s. of the derived, partially O-methylated alditol acetates. Each fraction contained 1–3 oligosaccharides, each of which had 2-acetamido-2-deoxy- -galactitol (GalNAc-ol) at the reduced end and involved one of the structures

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The majority of the oligosaccharides contained the unsubstituted “type 2” blood group precuisor-chain sequences, β- -Gal-(1→4)-β- -GlcNAc-(1→6) and single or repeating β- -Gal-(1→4)-β- -GlcNAc-(1→3), which are recognised by various anti-blood-group I and i cold agglutinins. The “type 1” sequence, β- -Gal-(1→3)-β-blood-group Ii activities, the following structural model can be proposed, which consists of (a) a core region; (b) a backbone region having (1→3)- and (1→6)-linked N-acetyl-lactosamine β-Gal-(1→4)-GlcNAc] branches with I activities, and linear, repeating, (1→3)-linked N-acetyl-lactosamine units with i activities; and (c) a peripheral region with blood-group isotype activities.

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