Structures of N-Linked Oligosaccharides of Microsomal Glycoproteins from Developing Castor Bean Endosperms

Abstract

The structures of sugar chains of the glycoproteins from the microsomal fraction of developing castor bean endosperms have been analyze. The structural analyses were done by a fluoresecence method combined with component analysis, exoglycosidase digestions, partial acetolysis, Smith degradation, and 1^H-NMR spectroscopy. The estimated structures fell into three categories; the first was oligomannose-type, the second xylomannose-type, the third complex-type. Among these oligosaccharides, Man₃Fuc₁Xyl₁GlcNAc₂ (M3FX) and Man₆GlcNAc₂ (M6B) were the major structures. The structures of Man₄GlcNAc₂ (M4C) and Man₄Xyl₁GlcNAc₂ (M4X) have also been found in the microsomal glycoproteins of the developing bean endosperms. These results could indicate that the structures of M4C, M4X, and M3FX are formed in the stage of sugar chain processing in the mirosomal fraction, in which oligomannose-type sugar chains are modified into complex-type ones by several kinds of processing enzymes.