A sialidase from the hepatopancreas of the shrimp Penaeus japonicus (Crustacea: Decapoda): reversible binding with the acidic beta-galactosidase.

1. The sialidase purified from the hepatopancreas of Penaeus japonicus is able to bind the acidic beta-galactosidase in vitro. No protective protein, Mr 32,000, was detected in either purified enzyme preparation. 2. The specific activity of the isolated sialidase is 55.0 mU/mg of protein. After polyacrylamide gel electrophoresis under denaturing conditions, the purified shrimp enzyme was found to consist of monomers of Mr 32,000. 3. The sialidase from shrimp has an isoelectric point (pI) of 4.6 +/- 0.1. 4. The shrimp enzyme has the pH optimum at 5.0 and its Km was 5.5 microM with 2'-(4-methylumbelliferyl)-alpha-D-N-acetylneuraminic acid as substrate. The enzyme activity was inhibited by either Hg2+ or Cu2+ ions.