The sorption parameters of glucoamylase on supersewn polymer carriers

Abstract

We previously used supersewn polymer sorbents for amylolytic enzymes immobilization. This type of sorbents has established itself as a promising carrier in the immobilization of macromolecules. The aim of this work is to study the sorption parameters of glucoamylase on supersewn sorbents MN-202 and MN-500. The sorption capacity of these supersewn polymer carriers with regard to glucoamylase depending
on the concentration of hydrogen ions in the solution was investigated. The protein concentration in the equilibrium solution was spectrophotometrically determined by the modified Lowry method. It was shown that the largest amount of protein is adsorbed at pH 4.5-5.0, i.e. in the region of the isoelectric point of glucoamylase, at which most of the enzyme exists in the form of a zwitter-ion. Isotherms of glucoamylase sorption on MN-202 and MN-500 carriers were obtained in the range of pH values corresponding to the maximum enzyme capacity (pH 4.7). It was noted that in the region of low concentrations (up to 6 ·10-4 mmol/l) sorption increases linearly with increasing protein concentration in the
equilibrium solution. Further, on the sorption isotherm, there is an inflection and a horizontal section corresponding to the formation of a polymolecular layer of the immobilized enzyme. The high specific surface area of the sorbents determines the possibility of π-π electron interaction between the sorbate and the sorbent matrix and promotes the formation of supramolecular complexes. IR spectroscopy was used to explain the nature of the interaction of glucoamylase with carriers. Adsorption isotherms of glucoamylase on polymer carriers were analyzed using the adsorption theory of BET. The equilibrium parameters of sorption were calculateded, i.e. the utmost amount of sorbated
glucoamylase, constants characterizing the interaction of the sorbate-sorbent and sorbate-sorbate types.The paper compares the properties of free and immobilized glucoamylase. The catalytic activity of glucoamylase was measured by photometric method. It is shown that the temperature optimum for both free and immobilized glucoamylase is 60-65 ° C, while the pH optimum of the heterogeneous biocatalyst expands.
Experiments on thermal inactivation showed that the heterogeneous biocatalyst has got increased resistance to denaturing effects of temperature and pH compared with the native enzyme. For the immobilized enzyme, a decrease in the inactivation constants in the entire studied temperature range (50-75°C) was noted, which indicates a greater stability of the immobilized enzyme.