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

Journal Article · Tue Mar 24 04:00:00 EST 1987 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00380a021· OSTI ID:6466605

May, S W; Herman, H H; Roberts, S F; Ciccarello, M C

The competence of dopamine ..beta..-monooxygenase (DBM) to process selenide substrates was investigated, in anticipation that the expected selenoxide products would exhibit unique reactivity and redox properties. The prototypical selenide phenyl 2-aminoethyl selenide (PAESe) was synthesized and shown to be a substrate for DBM with the characteristic e/O/sub 2/ ratio of 2:1 for monooxygenation. The kinetic parameters for oxygenation of PAESe were found to be similar to those for the DBM-catalyzed sulfoxidation of the cognate sulfide phenyl 2-aminoethyl sulfide, and selenoxidation was stimulated by fumarate in a manner similar to other well-characterized DBM monooxygenation reactions. Identification of phenyl 2-aminoethyl selenoxide (PAESeO) as the enzymatic product was accomplished by the demonstration of coincident elution of authentic PAESeO with the enzymatic product in three significantly different HPLC systems. PAESeO was found to oxidize ascorbic acid with the concomitant and stoichiometric reduction of PAESeO back to the selenide, PAESe. As a consequence of this nonenzymatic reaction, ascorbate-supported DBM turnover was prematurely terminated under standard assay conditions due to depletion of reduced ascorbate. The kinetics of the redox reaction between PAESeO and ascorbate were investigated with a spectrophotometric assay of ascorbate at 300 nm, and a second-order rate constant of 3.4 M/sup -1/ s/sup -1/ was determined at pH 5.0, 25/sup 0/C. Spectrophotometric assay of cytochrome c (cyt c) reduction at 550 nm during the oxidation of ascorbate by PAESeO demonstrated that no cyt c trappable semidehydroascorbate was produced in this nonenzymatic reaction.

• Research Organization: Georgia Institute of Technology, Atlanta
• OSTI ID: 6466605
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:6; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

560300* -- Chemicals Metabolism & Toxicology
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
AMINES
AROMATICS
ASCORBIC ACID
AUTONOMIC NERVOUS SYSTEM AGENTS
BARYONS
BIOCHEMICAL REACTION KINETICS
CARDIOTONICS
CARDIOVASCULAR AGENTS
CHALCOGENIDES
CHEMICAL REACTIONS
DOPAMINE
DRUGS
ELEMENTARY PARTICLES
ENZYMES
FERMIONS
HADRONS
HYDROXY COMPOUNDS
KINETICS
MAGNETIC RESONANCE
NEUROREGULATORS
NUCLEAR MAGNETIC RESONANCE
NUCLEONS
ORGANIC COMPOUNDS
OXIDATION
OXIDOREDUCTASES
OXYGENASES
PHENOLS
POLYPHENOLS
PROTONS
REACTION KINETICS
RESONANCE
SELENIDES
SELENIUM COMPOUNDS
STOICHIOMETRY
SYMPATHOMIMETICS
VITAMINS