Studies on the immobilized naringinase

Abstract

To remove the naringin which is the main bitter principle of grapefruit, naringinase was immobilized on porous glass by covalent bonding and its characteristics were studied. Crude form of naringinase produced from $\mbox{\underline{Aspergillus}}$ $\mbox{\underline{niger}}$ was partially purified by varous methods and immobilized to porous glass beads (96\% alkylamine derivative). About 40-70\% of initial naringinase activity was recovered after immobilization process. The optimum pH of the immobilized enzyme was the same as that of soluble enzyme; however, immobilized naringinzse showed a broader pH - activity profile than that of the soluble enzyme. pH dependence of stability of both was fairly similar up to pH 6.0, but above this pH the immobilized enzyme was more stable than the free enzyme. The optimal temperature shifted from 45$^\circ$C to 55$^\circ$C, and the thermal stability of the immobilized enzyme was better than that of the native naringinase. By immobilization, the activation energy of reaction was markedly decreased from 14.9 to 8.54 (kcal/gmole), and so was the apparent Km value from 2.2 to 0.86 (mM). Many experimental data in this work demonstrate the fundamental role played by diffusion in determining kinetic properties of immobilized naringinzse on glass bead. The deactivation rate of naringinase can be described by a simple methematical model derived from first-order deactivation and simple Michaelis Menten kinetics. At optimum conditions of immobilized naringinase (pH 5.0, 55$^\circ$C), the first-order decay constant was 0.0061 $hr^{-1}$ and the half life about 115 hrs. The activation energy of deactivation reaction was calculated as 2.38 Kcal/gmole. Increasing the reaction temperature results in an increase of the reaction rate, but it will be normally expected to promote the deactivation of the enzyme. Thus we attempted to determine the most economic temperature by computer simulation technique. As a computer simulation result, the decre...