An extracellular acid phytase was purified to homogeneity from the culture supernatant of the Saccharomyces cerevisiae CY strain by ultrafiltration, DEAE-Sepharose column chromatography, and Sephacryl S-300 gel filtration. The molecular weight of the purified enzyme was estimated to be 630 kDa by gel filtration. Removing the sugar chain by endoglycosidase H digestion revealed that the molecular mass of the protein decreased to 446 kDa by gel filtration and gave a band of 55 kDa by SDS-PAGE. The purified enzyme was most active at pH 3.6 and 40 degrees C and was fairly stable from pH 2.5 to 5.0. The phytase displayed broad substrate specificity and had a Km value of 0.66 mM (sodium phytate, pH 3.6,40 degrees C). The phytase activity was completely inhibited by Fe3+ and Hg2+, and strongly inhibited (maximum of 91%) by Ba2+, CO2+, Cu+, Cu2+, Fe2+, Mg2+, and Sn2+ at 5 mM concentrations. (C) 2008 Elsevier Ltd. All rights reserved.