초록
<P>An endo-polygalacturonase secreted by <I>Aspergillus sojae </I>was characterized after being purified to homogeneity from submerged cultures with orange peel as the sole carbon source by gel filtration and ion-exchange chromatographies. According to SDS-PAGE and analytical isoelectric focusing analyses, the enzyme presents a molecular weight of 47 kDa and pI value of 4.2. This enzyme exhibits considerable stability under highly acidic to neutral conditions (pH 1.5-6.5) and presents a half-life of 2 h at 50°C. Besides its activity towards pectin and polygalacturonic acid, the enzyme displays pectin-releasing activity, acting best in a pH range of 3.3-5.0. Thin-layer chromatographic analysis revealed that tri-galacturonate is the main enzymatic end product of polygalacturonic acid hydrolysis, indicating that it is an endo-polygalacturonase. The enzyme exhibits Michaelis-Menten kinetics, with K<SUB>M</SUB> and V<SUB>MAX</SUB> values of 0.134 mg/mL and 9.6 µmol/mg/min, respectively, and remained stable and active in the presence of SO<SUB>2</SUB>, ethanol, and various cations assayed except Hg<SUP>2+</SUP>.</P>