Purification and characterization of an acidic β‐galactosidase from the hepatopancreas of the shrimp Penaeus japonicus (Crustacea: Decapoda)

Abstract

An acidic beta-galactosidase was purified approximately 2,500-fold to homogeneity from the shrimp Penaeus japonicus, with a final specific activity of 4,000 units/mg of protein. SDS-polyacrylamide gel electrophoresis revealed the monomers of the acidic beta-galactosidase to have a relative mass of 66,000. Since the active acidic beta-galactosidase was found to have a relative mass of 140,000 by Ferguson plot analysis, the purified enzyme was concluded to be dimeric. No protective polypeptide was identified in the final preparation of purified beta-galactosidase. The shrimp enzyme was found to be thermolabile. Upon heating at 56 degree C for 10 min, the enzyme lost 50% of its activity. The acidic beta-galactosidase had an isoelectric point (PI) of 4.6 +/- 0.1 and the enzyme was sialyated. The shrimp enzyme had a pH optimum of 5.5 and its K(m) was 43 micrometer with 4-methylumbelliferyl-beta-D-galactoside as substrate. The enzyme was inhibited by both Mn(++) and Zn(++) ions.