An extracellular polygalacturonase (PGase) from Mucor rouxii NRRL 1894 was purified to homogeneity by two chromatographic steps using CM-Sepharose and Superdex 75. The purified enzyme was a monomer with a molecular weight of 43100 Da and a pI of 6. The PGase was optimally active at 35 degrees C and at pH 4.5. It was stable up to 30 degrees C and stability of PGase decrease rapidly above 60 degrees C. The extent of hydrolysis of different pectins was decreased with increasing of degrees of esterification. Except Mn2+, all the examined metal cations showed inhibitory effects on the enzyme activity. The apparent K-m and V-max values for hydrolyze of polygalacturonic acid (PGA) were 1.88 mg/ml and 0.045 mu mol/ml/min, respectively. The enzyme released a series of oligogalacturonates from polygalacturonic acid indicating that it had an endo-action. Its N-terminal sequence showed homologies with the endopolygalacturonase from the psychrophilic fungus Mucor flavus. (C) 2007 Elsevier Inc. All rights reserved.