COMPARATIVE-STUDY OF FREE AND MEMBRANE-BOUND ACIDIC BETA-DEUTERIUM-GLUCOSIDASE FROM THE HEPATOPANCREAS OF THE SHRIMP PENAEUS-JAPONICUS (CRUSTACEA, DECAPODA)

1. In the hepatopancreas of the shrimp Penaeus japonicus the beta-glucosidase is present, either free or membrane-bound. The specific activity of the purified enzyme is 237,333 units mg of protein and 191,111 units/mg of protein for the free and the membrane-bound beta-glucosidase, respectively. 2. The non-membrane-bound beta-glucosidase appears to be tie same molecular size as the membrane-bound enzyme, both being monomers and consisting of a polypeptide chain of apparent M(r) 65,000, as estimated by chromatography on Superose(TM) 12 and by SDS-PAGE. 3. Both enzymes share similarities in their molecular size and substrate specificities (with ratios of 100:17:4:12 for the non-membrane-bound and 100:32:13:12 for the membrane-bound enzyme for the activities with methylumbelliferyl-beta-D-glucoside, methylumbelliferyl-beta-D-galactoside, methylumbelliferyl-alpha-L-arabinopyranoside and methylumbelliferyl-beta-xyloside respectively, as substrates). 4. The membrane-bound beta-glucosidase can be differentiated from the non-membrane-bound enzyme by its isoelectric point (7.5 vs 6.6), K(m) (182-mu-M vs 76-mu-M), pH optimum (4.5 vs 5.5). phosphorylation, sialyation and thermostability.