THE EFFECT OF COPPER ON THE ACTIVITY OF CELLULASE AND BETA-GLUCOSIDASE IN THE PRESENCE OF MONTMORILLONITE OR AL-MONTMORILLONITE

We investigated the effect of copper on enzymatic decomposition of cel lulose by cellulase and beta-glucosidase in suspensions of montmorillo nite and aluminium-treated montmorillonite. The activity of both cellu lase and beta-glucosidase was found to be inhibited at copper concentr ations above 200 mu M. 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 beta-glucosidase, at copper concentrations of 200 mu M in comparison to copper-free assays.At pH 4, the presence of 200 mu M copper reduced the activities by 5% at mos t. Copper caused a shift of the pH optimum of both enzymes towards low er pH. Speciation calculations predicted that the enzymes are most sus ceptible 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, probabl y due to its larger specific surface and higher surface charge. Neithe r of the two minerals reduced the toxic effect of the metals. This res ult may be explained by the higher affinity of copper for cellulase an d beta-glucosidase than for montmorillonite or Al-montmorillonite. For both montmorillonite the combination with copper had a synergetic eff ect on the inhibition of enzymes activities. (C) 1998 Elsevier Science Ltd. All rights reserved.