3-Phenylpropenes as Mechanism-Based Inhibitors of Dopamine β-Hydroxylase: Evidence for a Radical Mechanism

Paul F. Fitzpatrick, Donald R. Flory, Joseph J. Villafranca

Research output: Contribution to journalArticle

39 Scopus citations

Abstract

A series of ring-substituted 3-phenylpropenes has been examined as mechanism-based inhibitors for the copper protein dopamine β-hydroxylase. p-HO-, p-CH30-, m-HO-, m-CH30-, p-Br-, and p-CN-substituted phenylpropenes all inactivate the enzyme under turnover conditions, requiring ascorbate and oxygen. Replacement of the benzylic hydrogens in 3-(p-hydroxyphenyl)propene with deuterium results in a kinetic isotope effect of 2.0 on kinact/KO2 but in no effect on the partition ratio, Vmax/kinact, consistent with a stepwise mechanism for hydrogen abstraction and oxygen insertion. The partition ratio is unchanged in the pH range from 4.5 to 7.1. Determination of the kinetics of inactivation and the partition ratios for each of these ring-substituted phenylpropenes has allowed determination of the respective V/KO2 values. A linear free energy plot of these values as a function of σ+ gives a p value of -1.2, while the partition ratios show only a slight decrease upon going from electron-donating to electron-withdrawing groups. The results are consistent with a mechanism for dopamine β-hydroxylase in which a hydrogen atom is abstracted to form a benzylic radical, which then partitions between hydroxylation and enzyme inactivation.

Original languageEnglish (US)
Pages (from-to)2108-2114
Number of pages7
JournalBiochemistry
Volume24
Issue number9
DOIs
StatePublished - Apr 1 1985

ASJC Scopus subject areas

  • Biochemistry

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