Methanococcus jannaschii ORF mj0608 Codes for a Class C Inorganic Pyrophosphatase Protected by Co2+ or Mn2+ Ions against Fluoride Inhibition

Openreading frame mj0608 of the Methanococcus jannaschii genome, recognized by its sequence similarity to that of the gene coding for class C inorganic pyrophosphatase in Bacillus subtilis, was cloned and over-expressed in Escherichia coli. The protein was purified and characterized by SDS–PAGE, Mr, and N-terminal sequence. Under suitable conditions it catalyzed the specific hydrolysis of PPi at about 600 μmol · min−1 · mg−1 at 25°C, and at 8000 μmol · min−1 · mg−1 at 85°C. Therefore this protein is a specific inorganic pyrophosphatase. The activities of Mg2+, Mn2+, Co2+, and Zn2+ ions as cofactors for hydrolysis of PPi were compared at pH 7.5 and 9.0. Unlike the class C pyrophosphatase of B. subtilis, this enzyme required no prior activation by low concentrations of Mn2+ or Co2+ ions. However, prior exposure to these ions afforded striking protection against inhibition by sodium fluoride, to which the enzyme was otherwise very sensitive.