Deuterium isotope effects in oxidation of dopamine by tyramine oxidase

We report the studies on the mechanism of oxidation of dopamine (DA) to 3',4'-dihydroxyphenylacetaldehyde (DOPAL) by enzyme tyramine oxidase (EC 1.4.3.6) using kinetic isotope effects (ME) and solvent isotope effects (SIB) methods. For kinetic studies, the selectively deuterium labelled isotopologues of dopamine, i.e., [(1R)-H-2]-, and [(1S)-H-2]-DA were used. The numerical values of KIE's for the (1R)- and (1S)-isotopologues of dopamine in the enzymatic oxidation of DA to DOPAL were determined using the non competitive spectrophotometric method. Also, the SIB's for this reaction carried out in heavy water were obtained spectrophotometrically. Some mechanistic details of enzymatic oxidation of DA to DOPAL were discussed.