Evidence that both protium and deuterium undergo significant tunneling in the reaction catalyzed by bovine serum amine oxidase

Journal Article · Tue Aug 08 00:00:00 EDT 1989 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00442a010· OSTI ID:5434411

Grant, K L; Klinman, J P ^[1]

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1. Univ. of California, Berkeley (USA)

The magnitudes of primary and secondary H/T and D/T kinetic isotope effects have been measured in the bovine serum amine oxidase catalyzed oxidation of benzylamine from 0 to 45{degree}C. Secondary H/T and D/T kinetic effects are small and in the range anticipated from equilibrium isotope effects; Arrhenius preexponential factors (A{sub H}/A{sub T} and A{sub D}/A{sub T}) determined from the temperature dependence of isotope effects also indicate semiclassical behavior. By contrast, primary H/T and D/T isotope effects, 35.2 {plus minus} 0.8 and 3.07 {plus minus} 0.07, respectively, at 25{degree}C, are larger than semiclassical values and give anomalously low preexponential factor rations, A{sub H}/A{sub T} = 0.12 {plus minus} 0.04 and A{sub D}/A{sub T} = 0.51 {plus minus} 0.10. Stopped-flow studies indicate similar isotope effects on cofactor reduction as seen in the steady state, consistent with a single rate-limiting C-H bond cleavage step for V{sub max}/K{sub m}. The comparison of primary and secondary isotope effects allows the authors to rule out appreciable coupling between the primary and secondary hydrogens at C-1 of the substrate. From the properties of primary isotope effects, they conclude that both protium and deuterium undergo significant tunneling in the course of substrate oxidation. These finding represent the first example of quantum mechanical effects in an enzyme-catalyzed proton abstraction reaction.

• OSTI ID: 5434411
• Journal Information: Biochemistry; (USA), Vol. 28:16; ISSN 0006-2960
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
AMINE OXIDASES
BIOCHEMICAL REACTION KINETICS
DEUTERIUM COMPOUNDS
ISOTOPE EFFECTS
TRITIUM COMPOUNDS
BLOOD SERUM
CARBON 14 COMPOUNDS
CATTLE
PROTONS
ANIMALS
BARYONS
DOMESTIC ANIMALS
ELEMENTARY PARTICLES
ENZYMES
FERMIONS
HADRONS
HYDROGEN COMPOUNDS
KINETICS
LABELLED COMPOUNDS
MAMMALS
NUCLEONS
OXIDOREDUCTASES
REACTION KINETICS
RUMINANTS
VERTEBRATES
550201* - Biochemistry- Tracer Techniques