Some properties of inorganic pyrophosphatase from Bacillus subtilis

Inorganic pyrophosphatase (pyrophosphate phosphohydrolase, EC 3.6.1.1; PPase) from Bacillus subtilis was purified to a homogeneous state electrophoretically when analysed by SDS-PAGE. The enzyme consists of six identical subunits; the molecular weight of the native enzyme estimated by gel filtration was approx. 120,000, and denaturing polyacrylamide gel electrophoresis gave a single band corresponding to 24,000. The enzyme absolutely required a divalent cation for its activity. Mg2+ was most effective, showing two steps of concentration-dependent activation. Mg2+ could be partially replaced by Mn2+ and Co2+. The enzyme was thermostable in the presence of Mg2+, and no loss of activity was observed on the incubation at 55 degrees C for an hour.