Article,
The action of chloride peroxidase on 4-chloroaniline. N-oxidation and ring halogenation.
Biochem J, 187 (3): 893--903 (June 1980)
Abstract
Chloride peroxidase catalyses both the ring halogenation and N-oxidation
reactions of 4-chloroaniline by H2O2 and either KCl or KBr. In the
absence of any halide salt only the N-oxidation reaction was observed,
with the resulting conversion of 4-chloroaniline into 4-chloronitrosobenzene.
The N-oxidation reaction proceeded even more rapidly in the presence
of Cl- or Br-, in spite of the fact that ring halogenation was also
a rapid reaction. The enhancement of N-oxidation was highly dependent
on the pH of the media and displayed an optimum in the region of
pH 3.5-4.0. No rate enhancement was observed above pH 5.5. KF partially
inhibited the rate of N-oxidation in a pH-dependent manner. On the
basis of calculated catalytic-centre activity the N-oxidation reaction
was the major reaction at pH 3.5 or higher, whereas the ring-halogenation
reaction became the major reaction below pH 3.5. In the presence
of high concentrations of 4-chloroaniline relative to H2O2 the reaction
intermediate, 4-chlorophenylhydroxylamine, was detected for the
first time in a chloride peroxidase-catalysed reaction with this
arylamine substrate. These findings were interpreted on the basis
of current knowledge concerning the mechanism of action of chloride
peroxidase.
