Membrane-bound N-acetyl-beta-glucosaminidase. Different binding specificity in control and I-cell disease livers

Several lysosomal enzymes solubilized at pH 4 from saponin-treated membranes showed markedly variable affinities to the bovine liver phosphomannosyl receptor in both bovine and human livers. The enzymes from I-cell disease liver did not bind the receptor in spite of normal intracellular activities. N-Acetyl-beta-glucosaminidase was effectively released from the membrane preparation of a control liver by mannose 6-phosphate, and other sugars showed little effect in this experiment. However, in the I-cell disease liver, dissociation occurred not by mannose 6-phosphate but by other sugars, such as fucose, mannose and N-acetyl-D-glucosamine. These results indicate the presence of an alternate transport system other than the pathway mediated by the mannose 6-phosphate receptor, and the role of other sugar-binding proteins is discussed in intracellular processing and transport of newly synthesized enzymes.