I-cell disease Desialylation of β-hexosaminidase and its effect on uptake by fibroblasts

The pinocytosis of fibroblasts of β-hexosaminidase (EC 3.2.1.30) excreted by cultured skin fibroblasts from a patient with I-cell disease was not enhanced by neuraminidase treatment of the enzyme. The uptake of sialic acid-rich normal plasma β-hexosaminidase was minimal and neuraminidase treatment did not appreciably enhance uptake. In contrast, sialic acid-rich normal seminal fluid β-hexominidase was readily pinocytosed regardless of neuraminidase treatment. Thus the presence of sialic acid on β-hexosaminidase does not influence uptake and a neuraminidase deficiency in I-cell disease may not be directly responsible for excessive extracellular enzyme.