Heavy metal ion inactivation of urease covalently immobilized on glutaraldehyde‐pretreated chitosan membrane was compared with that of free urease. The relative toxicity sequence of metal ions toward free urease: Hg2+ > Ag+ > Cu2+ > Ni2+ > Cd2+ > Zn2+ > Co2+ > Fe2+ > Pb2+ > Mn2+ correlates well with metal sulfide solubility product constants (except for Fe3+). The stability of urease against metal ion inactivation was considerably improved after immobilization: Ni2+, Co2+, Fe3+, Pb2+ and Mn2+ do not inactivate the immobilized urease in the range of concentrations at which free urease is thoroughly inactivated. Hg2+, Ag+, Cu2+, Zn2+ and Cd2+ inactivate the enzyme at considerably higher concentrations. The improved stability may be a consequence of structural changes introduced to the enzyme by the immobilization and of chelating effect of chitosan.
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Barbara Krajewska (1991) studied this question.
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