Purification and characterization of a novel type of catalase from the bacterium Klebsiella pneumoniae

A novel type of catalase, designated KpA, was purified from the bacterium Klebsiella pneumoniae. The enzyme is unique in that it is a dimer with subunit molecular weight of 80 000, it bears a chlorin-type heme as prosthetic group, and is active over a very wide range of H⁺ concentrations, with a plateau from pH 2.8 to 11.8. Yet, some properties of KpA are characteristic of typical catalases: it is stable when treated with ethanol/chloroform, cannot be reduced by dithionite and it is inhibited by 3-amino-1,2,4-triazole and by the conjugate acid forms of azide and cyanide. The protein of KpA is outstandingly resistant to denaturing conditions: it retains full activity when incubated with 8 M urea, at 30°C for 4 days, it is stable for 1 h at 70°C and at pH values 3.1 and 11.5 and, when dialyzed against 50 mM H₂O₂, it still retains 42% of its activity after 80 min.