Impaired degradation of chondroitin sulfate in GM2-gangliosidosis.

We have prepared a new radiolabeled substrate, derived from chondroitin 6-sulfate oligosaccharide, for the assaying of chondroitin sulfate degradation by beta-N-acetylgalactosaminidase. Using this substrate, we found a striking deficiency of beta-N-acetylgalactosaminidase activity in the cultured skin fibroblasts of patients with Sandhoff disease and Tay-Sachs disease. DEAE-cellulose chromatography at pH 6.0 revealed that both isoenzymes A and B of beta-N-acetylgalactosaminidases from normal human liver participated in the catabolism of chondroitin 6-sulfate. However, there were major differences in substrate specificity between isoenzyme A and isoenzyme B.