BETA-GLUCOSIDASE ACTIVITY IN THE PRESENCE OF COPPER AND GOETHITE

We investigated the effect of goethite and copper on almond P-glucosid ase activity. The activity of beta-glucosidase was found to be inhibit ed at dissolved copper concentrations exceeding 0.2 mM. Copper was mos t influential in the pH range 5-5.5, at which the enzyme activity was reduced by 50% or more at total copper concentrations of 0.2 mh I comp ared with copper-free assays. At pH 4, the presence of 0.2 mM copper r educed the activity by 15% at most. Copper caused a shift of the pH op timum towards lower pH. Goethite did not influence beta-glucosidase ac tivity significantly, although up to 95% of the enzyme was adsorbed on its surface. The adsorption seemed to be caused principally by non-el ectrostatic forces which were too weak to affect the structure of the enzyme. Goethite reduced the inhibitory effect of copper because of th e strong affinity of copper for goethite, as observed in batch adsorpt ion experiments. The sorption of the enzyme on goethite was not compet itive with copper at concentrations less than 0.2 mM: at larger concen trations, however, the presence of the enzyme reduced copper adsorptio n. The influence of copper on enzyme activity as well as the influence of copper in combination with goethite could be described with a mode l combining Michaelis-Menten enzyme kinetics with a simple conditional ly first-order reaction law for the binding of copper by the enzyme.