Structure of the carbohydrate units of IgE immunoglobulin. II. Sequence of the sialic acid containing glycopeptides

In a preceding paper it was shown than an IgE myeloma protein has 4 oligosaccharide units per heavy chain, 1 of which contains only mannose and N acetylglucosamine while the other 3 contain sialic acid, fucose, galactose, mannose, and N acetylglucosamine in the ratio of 1 to 2:1:2:3:4. The data in this paper establish the structure of the three sialic acid containing glycopeptides, designated B 1, B 2, and B 3. Glycopeptides B 2 and B 3 are branched structures containing two nonreducing termini, while B 1 has one nonreducing terminus with the above structure and another with a different sequence. The core of all three B glycopeptides is identical. The branch of B 1 terminating in sialic acid originates from position 3 of the β linked mannose in the core while the branch terminating in galactose originates from position 6 of this mannose.