test: enzyme (2.5 µM) was incubated at 30 °C (or 45 °C) with shaking for 30 minutes with Fre (1 µM), FAD (1 µM), NADH (2.5 mM), MgCl2 (10 mM) and substrate (0.5mM) in a total volume of 300 µL in 10 mM potassium phosphate buffer, pH 7.4, followed by HPLC