Deuterium isotope effects in oxidation of dopamine and norepinephrine catalyzed by horseradish peroxidase

Deuterium kinetic isotope effects (KIE’s) in the reaction of oxidation of dopamine (DA) catalyzed by the enzyme horseradish peroxidase (HRP, EC 1.11.1.7) was determined using a non-competitive spectrophotometric method. For kinetic studies, the deuterium ring labelled isotopomer [2’,5’,6’-2H3]-dopamine was synthesized using acid catalyzed isotopic exchange between authentic dopamine and heavy water. Deuterium solvent isotope effects (SIE’s) for dopamine and norepinephrine were determined separately for the enzymatic oxidation carried out in the presence or absence of hydrogen peroxide. Some mechanistic details of enzymatic oxidation of dopamine and norepinephrine to corresponding catecholchromes catalyzed by HRP were discussed.