An exopolygalacturonase [exo-PG; poly (1,4-alpha -D-galacturonide) digalacturonohydrolase, EC 3.2.1.82] was found in a culture of Bacillus sp. strain KSM-P576. The purified exo-PG had a molecular weight of approximately 115,000 and an isoelectric point of pH 4.6. The N-terminal amino acid sequence was Thr-Glu-Val-Ser-Pro-Lys-Ser-Pro-Ala-Ser-Pro-Val. Maximum activity toward polygalacturonic acid (PGA) was observed at 55 degreesC and pH 8.0 in 100 mM Tris-HCl buffer. The exo-PG was quite stable in various pH buffers between pH 6 and 12 when incubated at 30 degreesC for 1 h. Mg2+ Mn2+ Pd2+ and Ca2+ ions stimulated the enzyme activity. The exo-PG released digalacturonic acid from PGA, tri-, tetra-, and penta-galacturonic acids. The apparent K-m values for oligogalacturonic acids were almost identical, and k(cat) values increased with the chain length of the substrates.