Purification and properties of a high-molecular-weight, alkaline exopolygalacturonase from a strain of Bacillus

An exopolygalacturonase [exo-PG; poly (1,4-α-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°C 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°C 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 Km values for oligogalacturonic acids were almost identical, and kcat values increased with the chain length of the substrates.