THE GLYCANS OF SOYBEAN PEROXIDASE

Soybean hull peroxidase (SBP, E.C. 1.11.1.7), an anionic glycoprotein, was found to contain 18.2% carbohydrate with the average composition: 2 mol GlcNAc, 3.3 mol Man, 0.9 mol Fuc, and 0.7 mol Xyl, The oligosac charides of SBP, after release with glycopeptidase A, were investigate d by a combination of high pH anion exchange chromatography with pulse d amperometric detection, methylation analysis and matrix assisted las er desorption/ionization-time-of-flight mass spectrometry. The structu re of the major oligosaccharide, accounting for 60 to 65% of the total , is Man alpha 1 --> 6(Man beta 1 --> 3)(Xyl beta 1 --> 2)Man beta 1 - -> 4GlcNAc beta 1 --> 4(Fuc alpha 1 --> 3)GlcNAc, A further 20 to 25% of the released oligosaccharides belong to the (Xyl)(x)Man(m)(Fuc)(f)G lcNAc(2) (m = 2, 4, 5, 6; f = 0 or 1, x = 0 or 1) family, The rest of the oligosaccharides were of the high-mannose type, Investigation of t he six tryptic fractions containing carbohydrate revealed considerable heterogeneity in the N-linked oligosaccharides present in each fracti on, The major glycan (4, Table III) was present in each fraction, Two of the fractions contained the major part of the high-mannose type gly cans, Man(m)GlcNAc(2) (m = 5-9), the major species being Man(7)GlcNAc( 2). The other four fractions contained mainly members of the (Xyl)(x)M an(m)(Fuc)(f)GlcNAc(2) (m = 2, 4, 5, 6; f = 0 or 1; x = 0 or 1) family , Methylation analysis of the holo- and apo-SBP provide support for th e structures proposed for the oligosaccharides as well as for the hete rogeneity of the glycopeptide fractions.