Catabolism of N-glycosylprotein glycans: evidence for a degradation pathway of sialylglyco-asparagines resulting from the combined action of the lysosomal aspartylglucosaminidase and endo-N-acetyl-beta-D-glucosaminidase. A 400-MHz 1H-NMR study.

A mixture of sialylglycoasparagines and sialylglycopeptides was successively incubated with lysosomal extracts, at two pH values, first at pH 7.5 and then at pH 4. The 1H-NMR analysis of the sialyloligosaccharides released during the enzymatic digestion demonstrates the sequential action of aspartylglucosaminidase and an endo-N-acetyl-beta-D-glucosaminidase which release sialyloligosaccharides identical to the reference sugars isolated from the urine of patients suffering from sialidosis. This process represents a new catabolic pathway for N-glycosyl-proteins which may account for the appearance of the oligosaccharides stored in tissues and urine of patients suffering from lysosomal diseases.