Purification of an endo-polygalacturonase from Aspergillus niger

A pectinase was identified and isolated from a commercial Aspergillus niger pectinase preparation. The crude enzyme preparation, which was prepared by precipitation of the water extract of the culture of Aspergillus niger with ammonium sulfate, was further fractionated by three steps of chromatography of cation exchange, hydrophobic interaction and anion exchange to obtain an electrophoretically homogeneous pectinase. The molecular weight of the purified enzyme was estimated by SDS-PAGE to be 39.4 kD under non-reduced conditions and 41.8 kD under reduced conditions, with the optimum pH at 5.0, and the optimum temperature at 36?℃.