Properties of a novel periplasmic catalase–peroxidase from Escherichia coli O157:H7

A subset of catalase–peroxidases are distinguished by their periplasmic location and their expression by pathogens. Kinetic and spectral properties have not been reported for any of these enzymes. We report the cloning, expression, isolation, and characterization of KatP, a periplasmic catalase–peroxidase from Escherichia coli O157:H7. Absorption spectra indicated a mixture of heme states dominated by the pentacoordinate and hexacoordinate high-spin forms. Apparent kcat values for catalase (1.8 × 104 s−1) and peroxidase (77 s−1) activities were greater than those of other catalase–peroxidases. However, apparent KM values for H2O2 were also higher (27 mM for catalase and 3 mM for peroxidase). Ferric KatP reacted with peracetic acid to form compound I (8.8 × 103 M−1 s−1) and with CN− to form a ferri-cyano complex (3.9 × 105 M−1 s−1) consistent with other catalase–peroxidases. The isolation and characterization of KatP opens new avenues to explore mechanisms by which the periplasmic catalase–peroxidases may contribute to bacterial virulence.