OXIDATION OF AMINOPYRINE BY THE HYDROPEROXIDASE ACTIVITY OF LIPOXYGENASE - A NEW PROPOSED MECHANISM OF N-DEMETHYLATION

The oxidation of aminopyrine, an N-alkyl aromatic amine, by the hydrop eroxidase activity of lipoxygenase was studied. Aminopyrine gave rise to a purple color in the presence of H2O2 and lipoxygenase, the color being proportional to the aminopyrine radical cation. The H2O2/aminopy rine radical cation molar ratio was 0.5. The overall reaction was cons idered as an enzymic-chemical second order mechanism with substrate re generation. From the equations, the apparent constant of the radical c ation's decomposition (k'(app)) was evaluated under different experime ntal conditions. It was found to be inversely proportional to the prot on concentration but unaffected by the concentration of aminopyrine, T hese results suggest a new comprehensive mechanism for N-demethylation , which takes into account the described presence of both nitrogen- an d carbon-centered radicals and the marked effect of pH on the stabilit y of the radical cation. (C) 1997 Elsevier Science Inc.