Properties of acid phosphatase-tannic acid complexes formed in the presence of Fe and Mn

The preparation and characterisation of synthetic enzyme complexes simulati ng those usually encountered in soil were investigated. Complexes were prep ared at 30 degreesC by the interaction of acid phosphatase and tannic acid in the presence and absence of Fe and Mn ions (as chlorides) and oxides, wi th and without montmorillonite. In comparison with phosphatase-tannic acid complexes, the enzymatic complexes formed in the presence of Fe oxide showe d higher activity levels (>70%). Non significant increases were measured in the presence of Fe and Mn ions and Mn oxide. In the presence of montmorill onite, a further increase in the activity of the resulting complexes was me asured. For example, the activity of complexes formed with Fe3+ or Mn2+ inc reased by 25 and 28%, respectively. In all cases, the kinetics of the immob ilised enzyme conformed to the Michaelis-Menten equation and the V-max valu es were significantly (P = 0.001) lower and the K-m values significantly hi gher than those of the free enzyme. For example, a two-fold reduction in th e V-max and four-fold increase in the K-m parameters were measured for phos phatase complexed with tannic acid. In the presence of montmorillonite, no significant changes of V-max values were measured whereas a detectable redu ction of K-m values was observed. Immobilised phosphatase showed a greater sensitivity to increases in temperature, but higher stability to proteolyti c attack. Complexes with Fe ions and MnO2 were the most stable. (C) 2000 El sevier Science Ltd. All rights reserved.