Structure characterization of polypeptides of viscous glycoprotein from yam (Dioscorea opposita THUNB.) mucilage [Japanese]

摘要

In this study, partial structure of polypeptide chains of glycoprotein responsible for viscosity from three kinds of yams (Tsukuneimo, Ichoimo and Nagaimo) was characterized. The N-terminal amino acid sequences of 32- and 28-kDa glycoproteins obtained from SDS-PAGE in the absence of 2-mercaptoethanol (2-ME) were determined as V-E-D-E-F-S-Y-I-E-G-N-P-N-G-P-E-N-W-G-N. The N-terminal amino acid sequences of 56-kDa glycoproteins from Tsukuneimo and Ichoimo were identical, D-G-D-F-S-Y-I-E-G-S-P-N-G-P-E-N-W-G-N-L, whereas the N-terminal sequence (D-E-D-D-F-S-Y-I-E-G-S-P-N-G-P-E-N-W-G-N) for that from Nagaimo was different from it. On the database search via World Wide Web network, a consensus sequence, obtained from these sequences, was similar with that of dioscorin, one of the storage proteins of vam. On the SDS-PAGE in the presence of 2-ME, the glycoproteins demonstrated one peptide band with molecular mass of 32 kDa. Based on N-terminal amino acid sequence analysis. the 32-kDa peptide was identified as mixture of two kinds of polypeptides. designated as 32 kDa (A) for the dominant peptide and 32 kDa (B) for the minor peptide. Consequently three proteins obtained by non-reduced SDS-PAGE were concluded as follows; the 56-kDa glycoprotein consisted of two 32 kDa (B) joined by disulfide bond, the 32-kDa glycoprotein was monomer of 32 kDa (A) without any disulfide bonds, and the 28-kDa glycoprotein was monomer of 32 kDa (A) whose apparent molecular mass was decreased due to internal disulfide bond. The peptide mapping analysis using limited proteolysis and amino acid composition analysis for 32 kDa (A) peptide suggested that the glycoproteins of three yams had slightly different primary structure,.