Detection of alpha-glycosidic bonds in the ganglioside GM1 by stereospecific enzymatic degradation.

Abstract

The monosialosyl‐N‐tetraglycosyl‐ceramide (GM1) isolated from ox brain and submitted to a stepwise degradation by specific α‐ and β‐glycosidases isolated and purified from ox spleen. By the sequential action of β‐galactosidase and β‐N‐acetylhexosaminidase, 100% of the terminal galactose and the N‐acetylgalactosamine residues were removed, while the corresponding α‐glucosidases were completely ineffective. When the sialic acid was removed from the remaining sialated dihexosyl ceramide, the internal galactose residue becomes suspectible again to β‐galactosidase which removed up to 89%, but α‐galactosidase also hydrolyzed 2% of the internal galactose residues. A subsequent action of α‐glucosidase hydrolyzed 3% whereas β‐galactosidase released 47% of the remaining glucose moiety. The results reported prove a β‐configuration of the glycosidic‐linked terminal galactose and of the penultimate N‐acetylgalactosamine moiety of ganglioside GM1 throughout. A β‐configurated glycosidic linkage is also predominant for the internal galactose and the glucose residues, but the presence of a small percentage of α‐glycosidic bonds must be concluded from their susceptibility to α‐galactosidase and α‐glucosidase, respectively.