APPLICATION OF AN SH SURFACE ACOUSTIC-WAVE TO THE ANALYSIS OF CATALYSIS ON IMMOBILIZED GALACTOSE-OXIDASE

The surface acoustic wave (SAW) method, combined with measurements of reaction rates, was employed to investigate the role of the metal ion in the catalysis of a metalloenzyme. A device generating a shear horizontal leaky SAW was fabricated on which galactose oxidase (GAOD) was immobilized. The removal of Cu ions from immobilized GAOD to produce an inactive apoenzyme and its reverse process were monitored by changes in the SAW frequency. From the response in the SAW frequency during the oxidation of galactose, the formation of an enzyme-substrate complex was confirmed for GAOD, whereas the apoenzyme was found to have no capability of coordinating galactose, which was responsible for deactivation. Zn and Co ions were also accommodated in the apoenzyme to almost the same extent as Cu ions, but had no capability of coordinating galactose. It is concluded that the Cu ions control the coordination of galactose.