Interactions of invertase with tannic acid, hydroxy-aluminium (OH-A1) species or montmorillonite

Abstract

Interactions between invertase, tannic acid and hydroxy-aluminium (OH-A1) polymers were investigated with regard to their influence on enzyme activity and the formation of active enzymatic complexes. OH-A1 species slightly inhibited invertase activity (inhibition constant, K i = 133 him) whereas a marked inhibition (>90%) was detected at a tannic acid concentration greater than 1.25 mM. The V max and K m values indicated a pure non-competitive and a mixed-type inhibition mechanism of OH-A1 species and tannic acid, respectively. Depending on the incubation time and the tannic acid-to-enzyme ratio, the interaction between invertase and tannic acid yielded both soluble and insoluble complexes, which displayed reduced activity levels. The decrease of invertase activity was a function of both the tannic acid-to-invertase ratios and the contact time. Bonding between invertase and tannic acid as well as the residual activity of the immobilized enzyme were greatly increased by the presence of OH-A1 polymers during the complexation process. Many more active invertase molecules were removed from solution and an enhanced precipitation of active invertase-tannic acid complexes was observed. Clearly not only OH-A1 ions facilitated flocculation of tannate-invertase complexes with different structural characteristics but their interaction with tannic acid molecules gave rise to Al precipitation products having a different charge and sorption sites. Furthermore, an invertase-OH-Al-tannic acid complex was anchored on montmorillonite surfaces and the complex formed showed a relatively high enzymatic activity. OH-A1 species acting as bridges between tannate molecules and montmorillonite surfaces also facilitated the immobilization of soluble invertase-OH-Al-tannate complexes.