Use of isotope effects as a probe of enzyme reaction mechanisms
The use of multiple isotope effects has been extended to include both the variation of /sup 15/N isotope effects with deuterated and unlabeled substrates, and the use of solvent isotope effects in conjunction with /sup 13/C or /sup 15/N isotope effects. The deuterium isotope effect on the inhibition constant, /sup D/K/sub i/, of a competitive inhibitor has also been used to identify an active-site catalytic base. Phenylalanine ammonia lyase has been shown to catalyze the elimination of ammonia from the slow alternate substrate dihydrophenylalanine by an E1cb mechanism with a carbanion intermediate. This conclusion resulted from comparison of /sup 15/N isotope effects with 3-dideuterated and unlabeled substrates, and a deuterium isotope effect of 2.0 from dideuteration at C-3, with the equations for concerted, carbanion and carbonium ion mechanisms. Isotope effects with phenylalanine itself were smaller, but are also consistent with a carbanion mechanism, but with drastically increased commitments
- Research Organization:
- Wisconsin Univ., Madison (USA)
- OSTI ID:
- 5297562
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
ALANINES
AMINO ACIDS
AMMONIA
BIOCHEMICAL REACTION KINETICS
CARBON 13
CARBON ISOTOPES
CARBOXYLIC ACIDS
DEUTERIUM
ENZYME ACTIVITY
ENZYMES
EVEN-ODD NUCLEI
HYDRIDES
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPE EFFECTS
ISOTOPES
KINETICS
LIGHT NUCLEI
LYASES
NITROGEN 15
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NITROGEN ISOTOPES
NUCLEI
ODD-EVEN NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
REACTION KINETICS
STABLE ISOTOPES
SUBSTRATES
TRACER TECHNIQUES