Nitrogen isotope effects on glutamate decarboxylase from Escherichia coli

Journal Article · Tue May 03 04:00:00 EDT 1988 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00409a031· OSTI ID:7253223

Abell, L M; O'Leary, M H

The nitrogen isotope effect on the decarboxylation of glutamic acid by glutamate decarboxylase from Escherichia coli has been measured by comparison of the isotopic composition of the amino nitrogen of the product ..gamma..-aminobutyric acid isolated after 10-20% reaction with that of the starting glutamic acid. At pH 4.7, 37 /sup 0/C, the isotope effect is k/sup 14//k/sup 15/ = 0.9855 +/- 0.0006 when compared to unprotonated glutamic acid. Interpretation of this result requires knowledge of the equilibrium nitrogen isotope effect for Schiff base formation. This equilibrium isotope effect is K/sup 14//K/sup 15/ - 0.9824 for the formation of the unprotonated Schiff base between unprotonated valine and salicylaldehyde. Analysis of the nitrogen isotope effect on decarboxylation of glutamic acid and of the previously measured carbon isotope effect on this same reaction shows that decarboxylation and Schiff base formation are jointly rate limiting. The enzyme-bound Schiff base between glutamate and pyridoxal 5'-phosphate partitions approximately 2:1 between decarboxylation and return to the starting state. The nitrogen isotope effect also reveals that the Schiff base nitrogen is protonated in this intermediate.

• Research Organization: Univ. of Wisconsin, Madison (USA)
• OSTI ID: 7253223
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 27:9; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550601* -- Medicine-- Unsealed Radionuclides in Diagnostics
62 RADIOLOGY AND NUCLEAR MEDICINE
AMINO ACIDS
AMINOBUTYRIC ACID
AUTONOMIC NERVOUS SYSTEM AGENTS
BACTERIA
BIOCHEMICAL REACTION KINETICS
CARBON-CARBON LYASES
CARBOXY-LYASES
CARBOXYLIC ACIDS
DECARBOXYLASES
DRUGS
ENZYMES
ESCHERICHIA COLI
GLUTAMIC ACID
IMINES
ISOTOPE EFFECTS
ISOTOPES
KINETICS
LIGHT NUCLEI
LYASES
MICROORGANISMS
NEUROREGULATORS
NITROGEN 14
NITROGEN 15
NITROGEN ISOTOPES
NUCLEI
ODD-EVEN NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
REACTION KINETICS
SCHIFF BASES
STABLE ISOTOPES