Characterization of an anti-beta-galactosidase antibody recognizing a precursor but not a mature enzyme in solution

A monospecific antibody was raised against a recombinant human 84-kDa beta-galactosidase precursor protein, which had been produced with a baculovirus gene expression system and affinity-purified. It bound to the 64-kDa mature enzyme protein extracted from human fibroblasts and the antigenic recombinant precursor on immunoblotting, but neither the fibroblast-derived mature enzyme nor the 64-kDa mature protein-like tryptic product of the recombinant precursor protein was immunoprecipitated. We conclude that it specifically recognized the precursor but not the mature protein in solution. Immunoprecipitation with this anti-precursor antibody revealed that the precursor protein mainly accounted for the residual enzyme activity in fibroblasts from an adult GM1-gangliosidosis patient, and the mature protein accounted for the activity in fibroblasts from a juvenile GM1-gangliosidosis patient.