Adsorption of soil invertase to goethite, gibbsite and their organic complexes and the effects on enzyme catalytic performance

Abstract

Soil invertase plays important role in the enzyme-driven degradation of soil organic carbon, and influenced by the adsorption of minerals or clays. We studied the adsorption effects of goethite, gibbsite and their organic complexes (with tannic acid) on invertase, aiming to explore the influence on the mobility and catalytic behavior of invertase. Results showed that both minerals and mineral–tannic acid complexes (henceforth ‘complexes’) had considerable adsorption capacity for invertase and restricted its mobility. The catalytic performance of invertase was characterized. Under optimum conditions, the kinetics of the enzyme was reduced markedly after adsorption, indicating the decreased enzyme-substrate affinity. Adsorbed invertases retained 30.9–46.1% of the original activity and the mineral-adsorbed enzymes showed lower activities than the complex-adsorbed enzymes. All minerals and complexes had similar patterns on the influence on the pH and thermal properties of invertase, in which the adsorption improved the pH stability of the enzyme at various pH values, lowered the pH sensitivity and shifted the optimum pH towards the acid sites; while decreased thermal stability at various temperature values and higher temperature sensitivity of the adsorbed invertase were observed. In a 150-h incubation under soil–like conditions, all adsorbed invertases showed greater long–term stability than free invertase, and higher total activities (sum of adsorbed activities and dissolved activities) in adsorption system were observed after the incubation. These results implied that, in a soil microenvironment, the goethite, gibbsite and their organic complexes have a protection effect on invertase through adsorption.