Assay of NAD+-Isocitrate Dehydrogenase in Extracts of Bread Yeast with a Surface Acoustic Wave Impedance Sensor

The regulatory property of NAD+-Isocitrate dehydrogenase (NAD+-ICDH) was studied by means of a new device, a surface acoustic wave (SAW) impedance sensor, which comprises a 61MHz SAW resonator and a pair of parallel platinum electrodes. The NAD+-ICDH is an allosterically regulated enzyme which shows sigmoidal kinetic for DL-isocitrate. The Hill coefficient was estimated to be 2.93. A linear relationship between the frequency response and the enzyme concentration was obtained, and the experimental detection limit was evaluated to be 45mIU/ml. A comparison between the SAW impedance sensor and the conductometric method was carried out. The effects of AMP, ADP and ATP on the kinetic property of NAD+-ICDH were investigated; some other factors, such as the temperature and pH value, are also discussed.