Possible pathway for the processing of sugar chains containing xylose in plant glycoproteins deduced on structural analyses of sugar chains from Ricinus communis lectins

The structures of sugar chains from two lectins in seeds of the castor bean (Ricinus communis) were identified. The sugar chains were liberated from the lectins by hydrazinolysis. After N-acetylation, the reducing-end residues of the sugar chains were coupled with 2-aminopyridine. The pyridylamino derivatives thus obtained were purified by gel filtration and HPLC. The structures of the purified derivatives were identified by component sugar analysis, stepwise exoglycosidase digestion, partial acetolysis, and 500 MHz ¹H-NMR spectroscopy. A new processing pathway for sugar chains in plant glycoproteins was proposed on the basis of the structures of the sugar chains.