Physiological variant of antithrombin-III lacks carbohydrate sidechain at Asn 135

Both normal antithrombin-III (AT-III alpha) and the high heparin affinity form (AT-III beta) were isolated from pooled human plasma. AT-III beta had a lower negative charge and lower molecular mass than AT-III alpha. Sialidase and endo-F digestion indicated that the inherent difference resided in the oligosaccharide component of the molecule. CNBr fragmentation showed there was an oligosaccharide sidechain missing between residues 104 and 251, subdigestion with trypsin indicated that Asn 135 was not glycosylated in AT-III beta. Chromatography of total tryptic digests on concanavalin A-Sepharose confirmed that the high heparin affinity form of antithrombin lacked an oligosaccharide moiety at Asn 135.