NOVEL STRUCTURES OF N-LINKED HIGH-MANNOSE TYPE OLIGOSACCHARIDES CONTAINING ALPHA-D-GALACTOFURANOSYL LINKAGES IN ASPERGILLUS-NIGER ALPHA-D-GLUCOSIDASE

Seven oligosaccharides were isolated from alpha-D-glucosidase (EC 3.2. 1.20) from Aspergillus niger, and the structures of these oligosacchar ides were studied by H-1 NMR spectroscopy. After treatment of the alph a-D-glucosidase with N-glycosidase F, seven major oligosaccharide peak s were detected by Dionex anion-exchange HPLC. The structures correspo nding to the three peaks OS-1, OS-2, and OS-4 were determined to be Ma n8GlcNAc2, Man9GlcNAc2, and GlcMan9GlcNAc2, respectively, from H-1 NMR spectra of the isolated fractions. Each of the four oligosaccharides OS-5, OS-6, OS-7-1, and OS-7-2 contained an alpha-D-galactofuranosyl r esidue (Gal f) linked to Man (A) via an alpha-(1 --> 2)-linkage. OS-7 was found to consist of two oligosaccharides. The structures of these four oligosaccharides were determined to be Gal f Man5GlcNAc2, Gal f M an6GlcNAc2, Gal f Man7GlcNAc2, and Gal f Man8GlcNAC2 by H-1 NMR spectr oscopy and compositional analysis. The Gal f structure of Gal f Man5Gl cNAc2 was found to be identical to that of an oligosaccharide previous ly isolated from the a-D-galactosidase of the same strain1. The struct ure of OS-3 remains undetermined.