I-cell disease: evidence for a mannose 6-phosphate independent pathway for translocation of lysosomal enzymes in lymphoblastoid cells

Abstract

Soluble lysosomal enzymes are synthesized as precursors of higher molecular weight, and modified post-translationally at the polypeptide and oligosaccharide moieties [1,2]. The mannose 6-phosphate residue in the enzyme molecule is recognized by specific receptors, and translocated to lysosomes [2]. The enzyme-receptor complex is dissociated in the lysosome under conditions of low pH [2]. In I-cell disease, a defect of phosphorylation results in low or deficient activities of multiple lysosomal enzymes in cultured fibroblasts, which are released in the culture medium [3]. However, activities of lysosomal enzymes in various tissues are generally normal, except for P-galactosidase, and the presence of an alternate pathway other than the mannose 6-phosphate system has been suggested [4]. In this report, the possible mannose 6-phosphate system evaluated.