Interaction of acid phosphatase with clays, organic molecules and organo-mineral complexes: kinetics and stability

The properties of synthetic active enzymatic complexes, simulating those usually present in soil environment, were investigated. Complexes were formed by the interaction of acid phosphatase with clays (montmorillonite and Al hydroxide), tannic acid and organo-mineral aggregates, obtained by mixing tannate, OH-Al species and/or montmorillonite. Immobilized acid phosphatase showed catalytic features quite different from those of the free enzyme. The presence of OH-Al species in the matrix generally resulted in an improvement of some enzymatic properties. A gain in activity of about 45 and 55% was observed for the complexes acid phosphatase-tannate-OH-Al species after thermal deactivation at 60 degrees C and 2 h of exposure to proteinase K. High residual activities ranging from 17 to 61% and from 28 to 57% of the initial one were measured for complexes of the enzyme with inorganic and organic/organo-mineral matrices, respectively. In contrast, the association with a pure constituent such as montmorillonite and/or tannic acid gave rise to an immobilized enzyme, displaying a completely different catalytic behaviour. Compared to the free enzyme, acid phosphatase-montmorillonite and acid phosphatase-tannate complexes had a different pH-activity dependence and a higher and lower sensitivity to temperature and proteolysis, respectively. (C) 2000 Elsevier Science Ltd. All rights reserved.