The effect of copper on the activity of cellulase and β-glucosidase in the presence of montmorillonite or Al-montmorillonite

We investigated the effect of copper on enzymatic decomposition of cellulose by cellulase and β-glucosidase in suspensions of montmorillonite and aluminium-treated montmorillonite. The activity of both cellulase and β-glucosidase was found to be inhibited at copper concentrations above 200 μm. The influence of copper was strongest in the pH range 5–5.5. In this range, enzyme activities were reduced by 25% or more for cellulase, and by 50% or more for β-glucosidase, at copper concentrations of 200 μm in comparison to copper-free assays. At pH 4, the presence of 200 μm copper reduced the activities by 5% at most. Copper caused a shift of the pH optimum of both enzymes towards lower pH. Speciation calculations predicted that the enzymes are most susceptible to copper ions at high pH, where the involved amino acids are deprotonated. Both clay minerals strongly reduced enzyme activities. Montmorillonite had a stronger effect than Al-montmorillonite, probably due to its larger specific surface and higher surface charge. Neither of the two minerals reduced the toxic effect of the metals. This result may be explained by the higher affinity of copper for cellulase and β-glucosidase than for montmorillonite or Al-montmorillonite. For both montmorillonite the combination with copper had a synergetic effect on the inhibition of enzymes activities.