Enzymatic oxidation of phenothiazines by lipoxygenase/H2O2 system.
Lipoxygenase (LOX) (EC 1.13.11.12) oxidized a wide range of phenothiazine (Pt) tranquillizers to their corresponding radical cations in the presence of H2O2 by means of an enzymatic chemical second-order mechanism with substrate regeneration similar to that of horseradish peroxidase. The optimum pH of LOX for this hydroperoxidase activity was in the acid range (pH 3.0-4.0), as has been shown for other Pt oxidizing systems, such as peroxidase/H2O2 and haemoglobin. LOX showed Michaelis constants for Pt ranging from 1.4 to 8.5 mM and which, in some cases, e.g. trifluoperazine, displayed substrate inhibition. By contrast, it had a high affinity for H2O2 in the microM to mM range. A new, previously undescribed plot, which relates the enzymatic affinity and the apparent second-order decay of the cation radical, was developed to study the influence of the 2- and 10-substituents in the Pt ring. The implications of this new plot and the LOX-mediated Pt oxidation are also discussed.
Pérez-Gilabert
M
M
Departmento de Bioquímica y Biología Molecular-A, Facultad de Biología, Universidad de Murcia, Spain.
Sánchez-Ferrer
A
A
García-Carmona
F
F
D005609:Free Radicals; D006861:Hydrogen Peroxide / Q000737:chemistry*; D019746:Intramolecular Oxidoreductases; D007535:Isomerases / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008084:Lipoxygenase / Q000737:chemistry*; D010084:Oxidation-Reduction; D010640:Phenothiazines / Q000737:chemistry*; D013329:Structure-Activity Relationship; D015262:Xenobiotics / Q000378:metabolism
D005609:Free Radicals; D010640:Phenothiazines; D015262:Xenobiotics; D006861:Hydrogen Peroxide; D008084:Lipoxygenase; D007535:Isomerases; D019746:Intramolecular Oxidoreductases; C021377:hydroperoxide isomerase