Different effects of microwave energy and conventional heat on the activity of a thermophilic �-galactosidase fromBacillus acidocaldarius

The effect of microwave (f = 10.4 GHz) irradiation on a thermostable enzyme was experimentally tested, showing that irreversible inactivation is obtained. Enzymatic solutions (500 μl, with concentrations between 10–100 μg/ml) were exposed at 70 °C, at SAR levels of 1.1 and 1.7 W/g for 15, 30, 45, or 60 min, and their activity was compared to that of a sample heated in a water bath at the same temperature. The residual activity of the exposed samples depends on enzyme concentration, microwave power level, and exposure time; activity was reduced to 10% in 10 μg/ml solutions treated at 1.7 W/g for 60 min. Microwave effects disappeared at concentrations above 50 μg/ml. These results were not found following water bath heating at the same temperature and durations. Bioelectromagnetics 20:172–176, 1999.