Light and heavy lysosomes: characterization of N-acetyl-β-D-hexosaminidase isolated from normal and I-cell disease lymphoblasts.

We previously reported that I-cell disease lymphoblasts maintain normal or near-normal intracellular levels of lysosomal enzymes, even though -acetylglucosamine-1-phosphotransferase activity is severely depressed or absent (Little , 248, 151–159, 1987). The present study, employing subcellular fractionation on colloidal silica gradients, indicates that both light and heavy lysosomes isolated from I-cell disease and pseudo-Hurler polydystrophy lymphoblasts possess normal specific activity levels of -acetyl-β-D-hexosaminidase, α-D-mannosidase and β-D-glucuronidase. These current findings are in contrast to those of cultured fibroblasts from the same patients, where decreased intralysosomal enzyme activities are found. Column chromatography on revealed that N-acetyl-β-D-hexosaminidase in both heavy and light I-cell disease lysosomal fractions from lymphoblasts possesses an increased number of accessible galactose residues (30–50%) as compared to the enzyme from the corresponding normal controls. Endo-β--acetylglucos-aminidase H treatment of -acetyl-β-D-hexosaminidase from the I-cell lysosomal fractions suggests that the majority of newly synthesized high-mannose-type oligosaccharide chains are modified to complex-type carbohydrates prior to being transported to lysosomes. This result from lymphoblasts differs from previous findings with fibroblasts, where -acetyl-β-D-hexosaminidase from I-cell disease and pseudo-Hurler polydystrophy lysosomes exhibited properties associated with predominantly high-mannose-type oligosaccharide chains. The current results imply that different cell types may modify the carbohydrate side chains of lysosomal enzymes in a differential manner, and that selected cell types may also employ mechanisms other than the mannose-6-phosphate pathway for targeting lysosomal enzymes to lysosomes. [ABSTRACT FROM PUBLISHER]