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Kinetic Behavior of Synthetic Organo- and Organo-Mineral-Urease Complexes

Dipartimento di Scienze Chimico-Agrarie, Università di Napoli "Federico II", via Università 100-80055 Portici (Napoli), Italy

*Corresponding author (gianfred{at}vm.cised.unina.it).

ABSTRACT

A study was conducted for characterizing the properties and the catalytic behavior of enzymatic complexes that are considered analogues of those usually present in soil. Active enzymatic complexes were formed at 10°C by interaction for 1 h of urease and tannic acid with and without Fe ions and OH-Al polymers. The enzymatic complexes obtained in the presence of Fe³⁺ ions and OH-Al species showed higher activity levels than urease-tannate complexes. The pH optimum of immobilized urease did not differ significantly from that of free urease, except for the tannate complexes, which showed a pH optimum slightly shifted upwards by 0.5 units. Immobilized urease displayed the highest activity in a wider range of temperatures (60–80°C) compared with the free enzyme. The free enzyme showed a marked reduction in activity above 70°C. Higher values of energy of activation (E_a), enthalpy of activation (H_a), and the kinetic parameter (K_m) were obtained for urease immobilized on tannate molecules. On the contrary, the complexes obtained with Fe³⁺ and OH-Al species displayed kinetic and thermodynamic parameters similar to those of the free enzyme. Immobilized urease showed a catalytic behavior similar to the free enzyme, when the interaction with tannic acid occurred in the presence of Fe³⁺ ions and OH-Al polymers. Evidently, both Fe ions and OH-Al species favored the formation of enzymatic complexes in which conformational and catalytic features of the enzyme remained practically unchanged.

Received for publication March 24, 1994.

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