Mechanism-based inactivation of dopamine beta-hydroxylase by p-cresol and related alkylphenols
The mechanism-based inhibition of dopamine beta-hydroxylase by p-cresol (4-methylphenol) and other simple structural analogues of dopamine, which lack a basic side-chain nitrogen, is reported. p-Cresol binds DBH by a mechanism that is kinetically indistinguishable from normal dopamine substrate binding. Under conditions (pH 6.6) of random oxygen and phenethylamine substrate addition p-cresol adds randomly, whereas at pH 4.5 or in the presence of fumarate activator addition of p-cresol precedes oxygen binding as is observed with phenethylamine substrate. p-Cresol is shown to be a rapid (kinact = 2.0 min-1, pH 5.0) mechanism-based inactivator of DBH. This inactivation exhibits pseudo-first-order kinetics, is irreversible, is prevented by tyramine substrate or competitive inhibitor, and is dependent upon oxygen and ascorbic acid cosubstrates. Inhibition occurs with partial covalent incorporation of p-cresol into DBH. A plot of -log kinact vs. pH shows maximal inactivation occurs at pH 5.0 with dependence upon enzymatic groups with apparent pK values of 4.51 +/- 0.06 and 5.12 +/- 0.06. p-Cresol and related alkylphenols, unlike other mechanism-based inhibitors of DBH, lack a latent electrophile. These inhibitors are postulated to covalently modify DBH by a direct insertion of an aberrant substrate-derived benzylic radical into an active site residue.
- Research Organization:
- Smith Kline and French Laboratories, Philadelphia, PA
- OSTI ID:
- 6366565
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:9; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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560300* -- Chemicals Metabolism & Toxicology
59 BASIC BIOLOGICAL SCIENCES
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
AMINES
ANIMALS
AROMATICS
AUTONOMIC NERVOUS SYSTEM AGENTS
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL EFFECTS
CATTLE
CRESOLS
DOMESTIC ANIMALS
DRUGS
ENZYME ACTIVITY
ENZYMES
HYDROXY COMPOUNDS
HYDROXYLASES
HYDROXYLATION
INHIBITION
KINETICS
LABELLED COMPOUNDS
MAMMALS
ORGANIC COMPOUNDS
OXIDOREDUCTASES
PH VALUE
PHENOLS
REACTION KINETICS
RESPONSE MODIFYING FACTORS
RUMINANTS
STRUCTURE-ACTIVITY RELATIONSHIPS
SYMPATHOMIMETICS
TRITIUM COMPOUNDS
TYRAMINE
VERTEBRATES