Both normal antithrombin-III (AT-IIIα) and the high heparin affinity form (AT-IIIβ) were isolated from pooled human plasma. AT-IIIβ had a lower negative charge and lower molecular mass than AT-IIIα. 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-IIIβ. 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.
