Further facile immobilization of enzymes on hydrous metal oxides and use of their immobilization reversibility phenomena for the recovery of peptide antibiotics

Abstract

Practical aspects of the facile immobilization of enzymes on hydrous metal oxides, a well-established means of enzyme-movement restriction, are described. Various enzymes (e.g. glucoamylase, peroxidase, dextranase) have been immobilized by chelation of several hydrous metal oxides, those of titanium(IV) and zirconium(IV) proving to be the most satisfactory for practical purposes. Localization of the gel into a granular form could be achieved successfully with good enzyme-immobilization characteristics by using ion-exchange resin as an internal matrix. The immobilization process was highly efficient for the relative proportions of hydrous oxide to enzyme used, with usually >90% of the available protein being insolubilized. Retention of enzyme activity was generally very good and was stable to reuse and to conventional buffer conditions. Activities of the immobilized enzymes were partially stable to lyophilization or drying of the hydrous oxide gels. Modification of the hydrous metal oxide surface by drying or treatment with phosphate or carbonate led to a decrease in complexing ability. The effect of carbonate can be circumvented by lowering the pH of the solution to around 5 and removing any carbon dioxide formed, by aeration. Such treatment allowed compounds to chelate to hydrous zirconium oxide(IV) in the presence of carbonate and therefore the hydrous oxide could be applied successfully to the concentration of peptide antibiotics from the fermentation medium in which they are being produced, including production at low concentrations.