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The Mechanism of Zinc Inhibition of Glutamate Dehydrogenase Involves Subunit Communication
Author(s) -
Sinanan Leander,
Bell Ellis
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.792.13
Subject(s) - norvaline , zinc , chemistry , glutamate dehydrogenase , protein subunit , glutamate receptor , amino acid , tryptophan , biochemistry , enzyme , stereochemistry , biophysics , biology , organic chemistry , valine , receptor , gene
Zinc is a potent inhibitor of higher eukaryotic glutamate dehydrogenases. The mechanism of inhibition has previously been investigated using initial rate kinetic studies with either the dicarboxylic amino acid glutamate or the mono carboxylic alternative substrate norvaline. With glutamate zinc potently inhibits with the apparent affinity for zinc decreasing as the glutamate concentration decreases. With norvaline, no inhibition is seen. The goals of the current study were to quantitate the zinc binding, identify potential binding sites and determine whether or not zinc binding may be a] close to one of the three tryptophans in the protein, and b] induce conformational effects in the protein. Using the zinc sensitive chromophore 4‐par it is shown that zinc binds to glutamate dehydrogenase with a 1:1 stoichiometry with respect to polypeptide chains. Using tryptophan fluorescence spectroscopy it appears that zinc affects the most hydrophobic of the three tryptophans in the protein. Examination of the three dimensional structure of the enzyme raises the possibility that zinc binds at the subunit interface in the “twisty tie” region of the molecule. This is consistent with both the location of the most hydrophobic tryptophan and the fact that zinc appears to inhibit by disrupting subunit interactions necessary for full activity with glutamate as substrate. Supported by NSF grant MCB 0448905 to EB