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Human alpha 1-protease inhibitor has three oligosaccharide side chains attached
to 3 separate asparaginyl residues of the protein by N-glycosyl linkages. Two of
the three asparaginyl residues link mostly to the A-type oligosaccharide chains
which consist of Man3, Gal2, (GlcNAc)4 and (NeuAc)2. One of the three
asparaginyl residues also attaches to a B-type oligosaccharide chain, which
consists of Man3, Gal3, (GlcNAc)5, and (NeuAc)3. The ratio of A-chain to B-chain
in this particular position is about 2:1. The structures of A- and B-chains of
the glycoprotein were examined by periodate oxidation, sequential glycosidase
digestion, and permethylation. The results unequivocally revealed the following
structure for A-chains. (Formula: see text). B-type oligosaccharide chains have
an additional trisaccharide, i.e. NeuAc 2 alpha leads to 3 Gal 1 beta leads to 4
GlcNAc attached to mannose at the (a) and/or (b) position of A-type chains by a
beta 1 leads to 4 linkage. The sialic acid of human alpha 1-protease inhibitor
was determined to be N-acetylneuraminic acid.
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