To determine the molecular mass of the native enzyme, the freeze-dried proteins were resuspended in phosphate buffer, pH 7.0. Two hundred micrograms of the pure enzyme were loaded on size exclusion HPLC column Bio-Sil SEC 125 (300 × 7.8 cm; Bio-Rad) equilibrated in phosphate buffer. Elution was performed with phosphate buffer at 0.5 mL/min.