Identification of nonprotein ligands to the metal ions bound to glutamine synthetase
Electron paramagnetic resonance (EPR) was used to study the environment of Mn/sup 2 +/ bound to the tight (n/sub 1/) metal ion binding site of glutamine synthetase in the presence of analogues of the tetrahedral adduct, L-methionine (S)-sulfoximine (Met(O)(NM)-S) and L-methionine (R)-sulfoximine (Met(O)(NH)-R). The Mn/sup 2 +/ EPR spectrum in the presence of Met(O)(NH)-S is identical with the previously published spectrum obtained from a mixture of isomers and is characteristic of a highly octahedral metal ion environment with a small zero field splitting. The presence of Met(O)(NH)-R produces and EPR spectrum that appears characteristic of a more distorted metal ion environment, with a larger zero field splitting. These data demonstrate that the two isomers interact differently with the enzyme-bound Mn/sup 2 +/. Broadening of the Mn/sup 2 +/ EPR spectrum in the presence of Met(O)NH) is observed in /sup 17/O-enriched water due to superhyperfine coupling of water to the metal ion. Superhyperfine coupling due to the /sup 14/N nucleus of the imine nitrogen of the sulfoximine moiety of Met(O)(NH)-S but not of Met-(O)(NH)-R has been detected by electron spin-echo envelope modulation spectroscopy. Two intense peaks are evident in the presence of Met(O)(NH)-S with frequencies at 1.7 and 3.3 MHz. These peaks are absent when (/sup 15/N)imine-labeled Met(O)(NH) is used, indicating the presence of the sulfoximine nitrogen of Met(O)(NH)-S in the inner coordination sphere of the metal ion. Taken together, these results suggest a model of the active site in which the metal ion is directly involved in the catalytic mechanism, serving to stabilize the tetrahedral adduct formed from ammonia and ..gamma..-glutamyl phosphate.
- Research Organization:
- Pennsylvania State Univ., University Park
- OSTI ID:
- 5438282
- Journal Information:
- Biochemistry; (United States), Vol. 27:1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
62 RADIOLOGY AND NUCLEAR MEDICINE
LIGASES
CROSS-LINKING
MOLECULAR STRUCTURE
MANGANESE COMPOUNDS
CATALYSIS
CATIONS
ELECTRON SPIN RESONANCE
GLUTAMINE
HYPERFINE STRUCTURE
IMINES
ISOMERS
LIGANDS
METHIONINE
NITROGEN 15
OXYGEN 17
WATER
AMIDES
AMINO ACIDS
CARBOXYLIC ACIDS
CHARGED PARTICLES
CHEMICAL REACTIONS
DRUGS
ENZYMES
EVEN-ODD NUCLEI
HYDROGEN COMPOUNDS
IONS
ISOTOPES
LIGHT NUCLEI
LIPOTROPIC FACTORS
MAGNETIC RESONANCE
NITROGEN ISOTOPES
NUCLEI
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
POLYMERIZATION
RESONANCE
STABLE ISOTOPES
TRANSITION ELEMENT COMPOUNDS
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