Dopamine beta-hydroxylase. Demonstration of enzymatic ketonization of the product enantiomer S-octopamine.

Dopamine .beta.-hydroxylase: activity and inhibition in the presence of .beta.-substituted phenethylamines

“…In the case of X = OH, the rate of oxygen uptake in the presence of dopamine /3-hydroxylase approaches (and may exceed) rates observed with dopamine. Similar results have been reported recently by May et al (1981) for the oxidation of octopamine (X, Y = OH) by dopamine /3-hydroxylase.…”

“…The kinetic constants summarized in Table I represent a single oxygen concentration (0.2 mM); thus, depending on the magnitude of the Km for oxygen, the reported values reflect either km or k^JK0r Preliminary kinetic studies with /3hydroxyphenethylamine indicate very large values of Km for both /3-hydroxyphenethylamine, Km = 32 mM in the limit of 2 These are from the data in Table I and a molar molecular weight of 280000. Although May et al (1981) did not state the molecular weight used for calculation of and kM/Km, comparison of reported constants to enzyme specific activity indicates a value of 280000, as opposed to the subunit molecular weight of 70 000 used in Table I. We have assumed that (7?…”

Mechanism-based inactivation of dopamine .beta.-hydroxylase by p-cresol and related alkylphenols

“…Product analysis shows that an initial hydroxylation of p-cresol to 4-hydroxybenzyl alcohol occurs and that under conditions of prolonged turnover this is followed by an "overoxidation" of product to 4-hydroxybenzaldehyde. This is reminiscent of the oxidation of the unnatural S enantiomer of octopamine to the corresponding a-aminoacetophenone (May et al, 1981;Klinman & Krueger, 1982): An appreciable increase in Fmax(app) and a decrease in Km-(app) occur for p-cresol upon increasing oxygen substrate concentration from 0.24 to 1.14 mM. This suggests a higher dissociation constant KD for oxygen from the p-cresol ternary complex relative to that from the tyramine ternary complex.…”

Ascorbate depletion as a consequence of product recycling during dopamine .beta.-monooxygenase catalyzed selenoxidation

“…Dopamine 0-monooxygenase (DBM,1 EC 1.14.17.1), a copper-containing monooxygenase present in mammalian tissues (Levin & Kaufman, 1961;Friedman & Kaufman, 1965,1966, catalyzes the benzylic hydroxylation of dopamine to norepinephrine and thus plays a key role in neurotransmitter interconversion (Van der Schoot & Creveling, 1965; Skotland & Ljones, 1979;Rosenberg & Lovenberg, 1980; Villafranca, 1981) . Although DBM is traditionally viewed as a "specific hydroxylase", previous work in our laboratory has demonstrated several new kinetically facile monooxygenase activities for DBM: stereoselective sulfoxidation of phenyl aminoalkyl sulfides (May & Phillips, 1980;May et al, 1981b), oxygenative ketonization of benzylic S alcohols (May et al, 1981a(May et al, , 1982 , epoxidation of properly designed olefinic substrates (May et al, 1983;Padgette et al, 1985a), and oxidative N-dealkylation of a variety of molecules with benzylic amine functionalities (Padgette et al, 1984a(Padgette et al, , 1985a. In addition, DBM-catalyzed oxidative ketonization of /3-halophenethylamines has been reported (Klinman & Krueger, 1982; Mangold & Klinman, 1984), and alkyne oxidation has been reported by both us and Villafranca and co-workers (Colombo et al, 1984;Padgette et al, 1985a).…”

“…While the precise mechanism of the antihypertensive activity of these compounds is under active investigation, results on hand are consistent with a depletion of NE arising from competition with DA for DBM-catalyzed oxygenation. Similarly, we have recognized the pharmacological potential of DBM-targeted benzylic S alcohols as ketonizable prodrugs (May et al, 1981a), as well as the potential of modulating catecholamine levels via suicide inhibitors of DBM (Padgette et al, 1985a).…”