Haloperoxidase-Catalyzed Luminol Luminescence

Common peroxidase action and haloperoxidase action are quantifiable as light emission from dioxygenation of luminol (5-amino-2,3-dihydrophthalazine-1,4-dione). The velocity of enzyme action is dependent on the concentration of reactants. Thus, the reaction order of each participant reactant in lumin...

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Main Author: Robert C. Allen (Author)
Format: Book
Published: MDPI AG, 2022-03-01T00:00:00Z.
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Summary:Common peroxidase action and haloperoxidase action are quantifiable as light emission from dioxygenation of luminol (5-amino-2,3-dihydrophthalazine-1,4-dione). The velocity of enzyme action is dependent on the concentration of reactants. Thus, the reaction order of each participant reactant in luminol luminescence was determined. Horseradish peroxidase (HRP)-catalyzed luminol luminescence is first order for hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), but myeloperoxidase (MPO) and eosinophil peroxidase (EPO) are second order for H<sub>2</sub>O<sub>2</sub>. For MPO, reaction is first order for chloride (Cl<sup>−</sup>) or bromide (Br<sup>−</sup>). For EPO, reaction is first order for Br<sup>−</sup>. HRP action has no halide requirement. For MPO and EPO, reaction is first order for luminol, but for HRP, reaction is greater than first order for luminol. Haloperoxidase-catalyzed luminol luminescence requires acidity, but HRP action requires alkalinity. Unlike the radical mechanism of common peroxidase, haloperoxidases (XPO) catalyze non-radical oxidation of halide to hypohalite. That reaction is second order for H<sub>2</sub>O<sub>2</sub> is consistent with the non-enzymatic reaction of hypohalite with a second H<sub>2</sub>O<sub>2</sub> to produce singlet molecular oxygen (<sup>1</sup>O<sub>2</sub>*) for luminol dioxygenation. Alternatively, luminol dehydrogenation by hypohalite followed by reaction with H<sub>2</sub>O<sub>2</sub> yields dioxygenation consistent with the same reaction order. Haloperoxidase action, Cl<sup>−</sup>, and Br<sup>−</sup> are specifically quantifiable as luminol luminescence in an acidic milieu.
Item Description:10.3390/antiox11030518
2076-3921