Purification and Characterization of α-N-Acetylgalactosaminidase from Skipjack Liver

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Abstract
By means of a simple procedure involving two gel filtrations and an ion-exchange chromatography, a-iV-acetylgalactosaminidase was purified to an electrophoretically homogeneous form from skipjack liver, in which the enzyme is the dominant glyco-sidase. The final α- N -acetylgalactosaminidase preparation contained practically no other glycosidase activities except α-galactosidase activity, which amounted to 0.8% of the α- N -acetylgalactosaminidase activity and may be an intrinsic activity of the enzyme. The molecular weight of the enzyme was estimated to be 80,000 at pH 4.2 and 40,000 at pH 7.2 by molecular sieve chromatography, and to be 35,000 by SDS-polyacrylamide gel electrophoresis. The enzyme was most active at pH 4 and was inactive above pH 7. These results suggest that skipjack α- N -acetylgalactosaminidase exists as an active dimer at acidic pH and as inactive monomer at neutral or alkaline pH. The enzyme efficiently liberated the N -acetylgalactosamine unit from ovine submaxillary glycoprotein which had been desialylated by neuraminidase. The K m value and maximum velocity were 4.28 mM and 409μmol/min-mg for p-nitrophenyl α- N -acetylgalactosaminide, and 0.0543 mM and 1.19μmol/min-ing for ovine submaxillary asialoglycoprotein.