Effects of temperature and pH on the catalytic activity of the immobilizedbeta-galactosidase from Kluyveromyces lactis

A study of the cross-linking immobilization of P-galactosidase from Kluyver omyces lactis on graphite surfaces is reported here. The cross-linking reag ent was glutaraldehyde. Thermal deactivation of the immobilized enzyme at t he temperatures from 35 to 55 degreesC was investigated, and the deactivati on rate was found to follow the Arrhenius law with the activation energy of about 200 kJmol(-1) for the deactivation of the immobilized enzyme. The te mperature-activity curves are similar for both the free and immobilized enz yme. However, the maximum activity of the immobilized enzyme was shifted up from 40 degreesC to 50 degreesC compared with that of the free enzyme. The pH for the maximum activity of the immobilized enzyme to occur has been fo und to increase by 1.1 to 7.7 U compared with the free enzyme. Lactose hydr olysis in a skim milk using the immobilized enzyme has also been investigat ed in a continuous enzymatic reactor. The related mechanisms of the hydroly sis process are discussed. (C) 2001 Elsevier Science B.V. All rights reserv ed.