Purification and Properties of Peroxidase from Nitrosomonas europaea

Peroxidase from the obligate chemosynthetic bacteriumNitrosomonas europaea was purified 1,500-fold, and its properties were examined. The enzyme had a molecular weight of 53,000 and exhibited characteristic absorption maxima at 410, 524, and 558 mμ. The optimalp H and temperature were 7.5 and 44 C, respectively. The peroxidase reaction had an energy of activation of 5,850 cal/mole and required a primary substrate (H2 O2 ) concentration of 7 × 10−6 m to proceed at half maximal velocity (K m ). Reduced cytochrome,c,p -phenylenediamine and pyrogallol acted as hydrogen donors to the purified peroxidase-H2 O2 complex. Conditions most suitable for the chemical oxidation of ammonium by H2 O2 were determined. The reaction was rapid and produced nitrite but no nitrate. Hydroxylamine was not detected as an intermediate, but it could substitute for ammonium in the system. Neither the rate nor the extent of these reactions was influenced by purified peroxidase, and no evidence was obtained to support a conclusion that the enzyme performs a vital role in the transformation of ammonium to nitrite byN. europaea .