Polygalacturonase produced by Streptomyces lydicus was purified to homogeneity by ultrafiltration and a combination of ion exchange and gel filtration chromatographic procedures. The purified enzyme was an exo-polygalacturonase with a molecular weight of 43 kDa. It was optimally active at 50 degrees C and pH 6.0. The enzyme was stable from pH 4.0 to 7.0 and at or below 45 degrees C for 90 min. K value for polygalacturonic acid was 1.63 mg/mL and the corresponding V-max was 677.8 mu M min(-1) mg(-1). The inhibition constant (Ki) for gluconic acid D-lactone was 20.75 mM. Purified enzyme had been inhibited by N-bromosuccinimide, while L-tryptophan could induce enzyme activity, indicating the involvement of tryptophan at the active site. (c) 2007 Published by Elsevier Ltd.