Kinetic isotope effects on cytochrome P-450-catalyzed oxidation reactions: full expression of the intrinsic isotope effect during the O-deethylation of 7-ethoxycoumarin by liver microsomes from 3-methylcholanthrene-induced hamsters

Journal Article · Wed May 15 00:00:00 EDT 1985 · Arch. Biochem. Biophys.; (United States)

DOI:https://doi.org/10.1016/0003-9861(85)90822-7· OSTI ID:5079831

Miwa, G T; Harada, N; Lu, A Y

The intrinsic primary deuterium isotope effect for the O-deethylation of 7-ethoxycoumarin has been estimated by the Northrop method for the microsomal cytochrome P-448 system from 3-methylcholanthrene-induced hamster livers. The intrinsic isotope effect (Dk = 5.5) was found to be equivalent to the observed deuterium isotope effect, demonstrating that the isotope effect for this reaction was fully expressed by this cytochrome P-448 system. These data unequivocally demonstrate that C-H bond cleavage is the rate-limiting step in the overall reaction catalyzed by this system. The decrease in the rate of product formation, occurring as a consequence of deuterium substitution, resulted in a reduction in the quantity of substrate metabolized but was not accompanied by the change in regiospecificity observed in previous studies with a hepatic cytochrome P-448 isozyme purified from 3-methylcholanthrene-induced rats. These data demonstrate that the catalytic site of the hamster isozyme(s) offers more constraints to 7-ethoxycoumarin reorientation than does the catalytic site of the rat liver isozyme.

• OSTI ID: 5079831
• Journal Information: Arch. Biochem. Biophys.; (United States), Vol. 1
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
CHOLANTHRENE
METABOLIC ACTIVATION
COUMARINS
ISOTOPE EFFECTS
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL MODELS
CYTOCHROMES
DEUTERIUM
HAMSTERS
ISOENZYMES
LIVER
MICROSOMES
RATS
REDOX PROCESS
SUBSTRATES
ANIMALS
ANTICOAGULANTS
AROMATICS
BODY
CELL CONSTITUENTS
CONDENSED AROMATICS
DIGESTIVE SYSTEM
DRUGS
GLANDS
HEMATOLOGIC AGENTS
HYDROGEN ISOTOPES
ISOTOPES
KINETICS
LIGHT NUCLEI
MAMMALS
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANOIDS
ORGANS
PIGMENTS
REACTION KINETICS
REPROCESSING
RODENTS
SEPARATION PROCESSES
STABLE ISOTOPES
VERTEBRATES
550201* - Biochemistry- Tracer Techniques