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Formation and Activity of Urease-Tannate Complexes Affected by Aluminum, Iron, and Manganese

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

The formation of active enzymatic complexes, obtained by the interaction of urease, tannic acid, and soluble and insoluble species of Al, Fe, or Mn, was studied. Tannic acid strongly inhibited urease activity (inhibition constant, K_i = 0.040 mM). The dependence of kinetic parameters (V_max and K_m) on tannic acid concentration suggests a pure uncompetitive inhibition mechanism. Soluble and insoluble urease-tannate complexes were formed by increasing both the contact time and the tannic acid/urease ratios. Soluble (FeCl₃, MnCl₂, and OH-Al polymers) and insoluble (Fe₂O₃ and MnO₂) inorganic components differently influenced the interaction of urease with tannic acid molecules and the residual activity of the immobilized enzyme. An increased removal of urease molecules from solution as well as an enhanced residual enzymatic activity of urease complexes was observed in the presence of all the additives. Soluble species (FeCl₃ and OH-Al polymers) probably acted as flocculating agents or promoted the formation of more active enzymatic complexes. On the contrary, MnO₂ showed a predominant polymerizing action on tannate molecules that gave rise to insoluble aggregates occluding urease molecules. Adsorption, as opposed to polymerization, probably occurred in the presence of Fe₂O₃.

Received for publication March 24, 1994.