Kinetic studies on beta-fucosidases of Achatina balteata

beta-Fucosidases (beta-D-fucoside fucohydrolase, EC 3.2.1.38) isolated from the digestive juice of Achatina balteata catalyze hydrolysis of beta-D-fucosides, beta-D-glucosides and beta-D-galactosides but the values of kinetic parameters show that catalytic efficiency is maximum towards beta-D-fucosides. The results of mixed substrate incubation studied and inhibition by glycopyranoses indicate that there is at least one site at which all tested substrates are hydrolyzed. In the absence of inhibitor, the reciprocal plots exhibit a significant downward curvature. If a substrate analogue is present, the plots can be straight lines. These results are consistent with the presence on the enzyme molecule of at least two distinct sites for the substrate molecules, one being an active site and the other being either a second active site with different kinetic parameters or a modifier site. Also data are shown to fit quite well with the mechanism proposed for a mnemonic enzyme.