The precursor of acid alpha-glucosidase is synthesized as a membrane-bound enzyme.

A pulse-chase study in human skin fibroblasts showed that a 110 kDa precursor of acid alpha-glucosidase was synthesized as a membrane-bound protein, which was solubilized in vitro not by mannose 6-phosphate or 1M KCl but by Triton X-100 or trypsin. This 110 kDa precursor form bound to the membrane was detected in control fibroblasts treated with tunicamycin and in I-cell disease fibroblasts as well. The precursors in human placenta were found also in the membrane fraction. It was concluded that the newly synthesized acid alpha-glucosidase precursor is located on the surface of the membrane, and the phosphomannosyl receptor does not participate in the enzyme-membrane binding.