Periodate oxidation and Smith degradation of desialized human erythrocyte
glycoproteins lead to an almost complete destruction of galactose and some loss of
galactosamine and glucosamine. Neutral sugar and hexosamine content of native MN substances
are only slightly influenced by periodate oxidation. Destruction of galactose is
accompanied by an uncovering of A-like receptor sites detectable by agglutinins from
plants and snails, which are directed against terminal N-acetylgalactosamine. From the
specificity of these antibody-like substances, it is deduced that the amino sugar functioning
as receptor is α-glycosidically linked. Destruction of the receptor sites by subsequent
alkaline borohydride treatment suggests that the N-acetylgalactosamine is unmasked by
degradation of the alkali-labile tetrasaccharide of human erythrocyte glycoproteins.
Periodate-oxidized and Smith-degraded NANA-free erythrocyte and ovarian cyst glycoproteins
treated by acetolysis are potent inhibitors of anti-Tn from man, animals, and
plants, suggesting that Tn-antigen is represented by terminal, α-glycosidic, peptide-bound
N-acetylgalactosamine. It is concluded that Tn-antigen is probably a cryptic determinant
of the alkali-labile tetrasaccharide, which has been isolated from human erythrocyte
glycopeptides.
The nature of the receptor sites for several agglutinins is characterized by
hemagglutination inhibition assays. The inhibitory activity of human erythrocyte glycoproteins,
from which sialic acid, sialic acid and galactose or alkali-labile oligosaccharides
have been removed, is compared to the inhibitory effect of compounds with known
structure. It is shown that the lectin from Arachis hypogea and anti-T bind to alkali-labile
galactosyl-residues. Agglutinins from Bauhiniapurpurea and variegata (non- or N-speciflc),
Maclura aurantiaca, Iberis amara, sempervirem, umbellata hybrida and umbellata nana
(M- or nonspecific), Moluccella laevis (A- plus N-specific), Helix pomatia, Helix aspersa,
Helix lucorum and Caucasotachea atrolabiata interact with alkali-labile V-acetylgalactosamine.
The results obtained with the anti-A agglutinins from various snails suggest that
human erythrocyte glycoproteins contain, besides the alkali-labile tetrasaccharide, a
peptide-linked sialyl-N-acetyl-galactosaminyl-residue. The investigations do not allow a
precise definition of the receptor sites for the lectins having M- or N-specificity.
It is shown that M-active glycoproteins react de novo with anti-N lectins
from Vicia graminea and Bauhinia purpurea after blocking of free amino and carboxyl
groups. The significance of this phenomenon is briefly discussed.
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