Activite des complexes acides humiques-invertase: Influence du mode de preparation

During the preparation of insoluble humic acid-invertase-Ca²⁺ complexes, the humic acid, enzyme and Ca²⁺ concentrations were varied as well as the time of contact between the organic and the cation, and the order in which these three substances were added. The enzymatic activities of these complexes are very different. In complexes obtained at pH 7.0, adding humic acids first, then invertase and finally Ca²⁺, the enzyme molecules probably occur in two forms: some may be fixed on the surface, either by adsorption or covalence, the others may be trapped in a micellar net. The initial catalytic activity and lifetime of the complexes depends on the relative abundance of the three substances and on the time of contact. The kinetics of the first type of complex is divided into three parts. During the first very short period, a strong inactivation is noticed which can be explained in terms of three phenomena: separation of some micellae bound to enzyme molecules, discharge of trapped invertase molecules because of destructuring of the net after loss of micellae, desorption of the enzyme. The intermediate phase corresponds to a greater cohesion of the net since the loss of organic matter is reduced and the inactivation is slower; its length depends on the preparation. The final phase begins when the complex is free from labile fractions: it represents the residual activity of the complex and develops very slowly.If insoluble humate suspensions are used rather than humic acids solutions, the formation of humateinvertase complexes proceeds essentially by adsorption at the surface of the support. The kinetics of the catalytic activity of such enzymatic complexes is similar to that of desorption.