Human liver lysosomal alpha-glucosidase modified by chemical galactosylation and isolation of specific antibodies

Human liver acid alpha-glucosidase (1,4-alpha-D-glucan glucohydrolase, EC 3.2.1.3) was modified with water soluble carbodiimide in the presence of p-aminophenyl-beta-D-galactopyranoside. The incorporation of the aminophenyl derivative of galactose into alpha-glucosidase caused some changes in the physiocochemical properties of the enzyme: a blue shift in the absorption maximum, an alteration of the total electric charge affecting electrophoretic mobility upon polyacrylamide gel electrophoresis, and acquisition of the ability to interact specifically with Ricinus communis agglutinin. At the same time, the 'galactosylated' enzyme possessed high stability and exhibited catalytic activity towards maltose. The Km values of the native and modified enzymes with maltose were 6 and 5 mM, respectively. p-Aminophenyl-beta-D-galactopyranoside residues incorporated in alpha-glucosidase and in other proteins were found to be antigenic determinants to which the pure antibodies were obtained.