Mechanism-based inactivation of dopamine beta-monooxygenase by beta-chlorophenethylamine.
Functionalization of the beta-carbon of phenethylamines has been shown to produce a new class of substrate/inhibitor of dopamine beta-monooxygenase. Whereas both beta-hydroxy- and beta- chlorophenethylamine are converted to alpha-aminoacetophenone at comparable rates, only the latter conversion is accompanied by concomitant enzyme inactivation ( Klinman , J. P., and Krueger , M. (1982) Biochemistry 21, 67-75). In the present study, the nature of the reactive intermediates leading to dopamine beta-monooxygenase inactivation by beta- chlorophenethylamine has been investigated employing kinetic deuterium isotope effects and oxygen- 18 labeling as tools. Mechanistically significant findings presented herein include: 1) an analysis of primary deuterium isotope effects on turnover, indicating major differences in rate-determining steps for beta-chloro- and beta- hydroxyphenethylamine hydroxylation, Dkcat = 6.1 and 1.0, respectively; 2) evidence that dehydration of the gem-diol derived from oxygen- 18-labeled beta- hydroxyphenethylamine hydroxylation occurs in a random manner, attributed to dissociation of enzyme-bound gem-diol prior to alpha-aminoacetophenone formation; 3) the observation of a deuterium isotope effect for beta- chlorophenethylamine inactivation, Dkinact = 3.7, implicating C--H bond cleavage in the inactivation process; and 4) the demonstration that alpha-aminoacetophenone can replace ascorbic acid as exogenous reductant in the hydroxylation of tyramine. As discussed, these findings support the intermediacy of enzyme-bound alpha-aminoacetophenone in beta- chlorophenethylamine inactivation, and lead us to propose an intramolecular redox reaction to generate a ketone-derived radical cation as the dopamine beta-monooxygenase-inactivating species.
D015078:2-Hydroxyphenethylamine / Q000378:metabolism; D000098:Acetophenones / Q000378:metabolism; D004299:Dopamine beta-Hydroxylase / Q000037:antagonists & inhibitors*; D007700:Kinetics; D008956:Models, Chemical; D010627:Phenethylamines / Q000494:pharmacology*
D000098:Acetophenones; D010627:Phenethylamines; C041830:2'-chlorophenethylamine; C024324:phenacylamine; D015078:2-Hydroxyphenethylamine; D004299:Dopamine beta-Hydroxylase