TY - JOUR
T1 - 3-Phenylpropenes as Mechanism-Based Inhibitors of Dopamine β-Hydroxylase
T2 - Evidence for a Radical Mechanism
AU - Fitzpatrick, Paul F.
AU - Flory, Donald R.
AU - Villafranca, Joseph J.
PY - 1985/4/1
Y1 - 1985/4/1
N2 - 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.
AB - 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.
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U2 - 10.1021/bi00330a003
DO - 10.1021/bi00330a003
M3 - Article
C2 - 3995005
AN - SCOPUS:0021799987
VL - 24
SP - 2108
EP - 2114
JO - Biochemistry
JF - Biochemistry
SN - 0006-2960
IS - 9
ER -