Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P04040 (Catalase)
 3,577 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Intramolecular isotope effects were determined for the N-demethylation of N-methyl-N-trideuteriomethylaniline catalyzed by two isozymes of cytochrome P-450 and several peroxidases in order to differentiate between deprotonation and hydrogen atom abstraction steps. Lactoperoxidase, hemoglobin, myoglobin, and two isozymes of horseradish peroxidase catalyzed the hydroperoxide-dependent N-demethylation at initial rates ranging from 20 to 1700 min-1. These hemeproteins exhibited large and comparable intramolecular isotope effects (kH/kD = 8.6 to 10.1). In contrast, two isozymes of cytochrome P-450 as well as chloroperoxidase (v = 1.5 to 1700 min-1) gave low isotope effects (kH/kD = 1.7 to 3.1) under identical conditions. Catalase exhibited an intermediate intramolecular isotope effect (kH/kD = 5.4). These results have been interpreted to indicate that most of the hemeproteins investigated catalyze N-demethylation reactions via alpha-carbon hydrogen atom abstraction, while the reactions catalyzed by cytochrome P-450 and chloroperoxidase proceed via alpha-carbon deprotonation.
 ...
PMID:The use of intramolecular isotope effects to distinguish between deprotonation and hydrogen atom abstraction mechanisms in cytochrome P-450- and peroxidase-catalyzed N-demethylation reactions. 664 95

The peroxidase-supported N-demethylations catalyzed by chloroperoxidase, a heme protein isolated from Caldariomyces fumago, have been investigated as models for cytochrome P-450-catalyzed N-dealkylations. The turnover number for the ethyl hydrogen peroxide-supported dealkylation of N,N-dimethylaniline by chloroperoxidase (1476) was much greater than that for cytochrome P-450-catalyzed dealkylations. The dealkylations of N,N-dimethylaniline by chloroperoxidase yielded N-methylaniline and formaldehyde in equimolar amounts with no other products detectable by high pressure liquid chromatography analysis of the reaction mixture. Ethyl hydrogen peroxidase could be replaced by other hydroperoxides, peroxides, or peracids. Chloride ions stimulated the reaction at low pH. The dealkylation reaction exhibited normal Michaelis-Menten saturation kinetics with respect to N,N-dimethylaniline (Km = 0.08 mM) and ethyl hydrogen peroxide (Km = 0.8 mM) at low substrate concentrations. However, substrate inhibition occurred at higher concentrations of N,N-dimethylaniline. The chloroperoxidase-catalyzed demethylations were inhibited by inhibitors of cytochrome P-450 such as azide or n-propyl gallate, but not by metyrapone, SKF-525A, or piperonyl butoxide. Although tiron and DL-epinephrine, trapping agents for the superoxide anion, inhibited the demethylation reactions, superoxide dismutase had no effect. There was no significant inhibition by alpha-phenyl-t-butyl-nitrone or 5,5-dimethyl-pyrroline-N-oxide, which react with free radicals. Diphenylfuran and DL-histidine, which react with singlet oxygen, did not inhibit the reaction. Substitution of D2O for H2O resulted in a marked inhibition with a solvent isotope effect (VH/VD) of 3.6. Chloroperoxidase did not catalyze the demethylation of N,N-dimethylaniline-N-oxide, indicating that the reaction does not proceed via an N-oxide intermediate.
 ...
PMID:N-Demethylation reactions catalyzed by chloroperoxidase. 719 53