title: Spectrochemical evidence for the presence of a tyrosine residue in the allosteric site of glucosamine-6-phosphate deaminase from Escherichia coli.
abstract: The interaction of the enzyme glucosamine 6-phosphate deaminase from Escherichia coli with its allosteric activator, N-acetyl-D-glucosamine 6-phosphate, was studied by different spectrophotometric methods. Analysis of the circular-dichroism differential spectra produced by the binding of the allosteric activator or the competitive inhibitor 2-amino-2-deoxy-D-glucitol 6-phosphate (a homotropic ligand displacing the allosteric equilibrium to the R conformer), strongly suggests the presence of tyrosine residues at or near the allosteric site, although a conformational effect cannot be ruled out. The involvement of a single tyrosine residue in the N-acetyl-D-glucosamine-6-phosphate binding site of glucosamine-6-phosphate deaminase was supported by spectrophotometric pH titrations performed in the presence or absence of the homotropic and heterotropic ligand. In these experiments, a single titrated tyrosine residue is completely protected by saturation with the allosteric activator; this group is considerably acidic (pK 8.75). The analysis of the amino acid sequence of the deaminase using a set of indices for the prediction of surface accessibility of amino acid residues, suggests that the involved residue may be Tyr121 or Tyr254.
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Distrito Federal, Mexico.
authors.forename: M M
authors.initials: MM
authors.lastname: Altamirano
authors.forename: A
authors.initials: A
authors.lastname: Hernandez-Arana
authors.forename: S
authors.initials: S
authors.lastname: Tello-Solis
authors.forename: M L
authors.initials: ML
authors.lastname: Calcagno
mesh_terms: D019747:Aldose-Ketose Isomerases; D000495:Allosteric Site; D000595:Amino Acid Sequence; D002238:Carbohydrate Epimerases / Q000737:chemistry* / Q000302:isolation & purification; D002942:Circular Dichroism; D004926:Escherichia coli / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D011487:Protein Conformation; D013056:Spectrophotometry, Ultraviolet; D014443:Tyrosine
chemical_list: D014443:Tyrosine; C020582:glucosamine-6-phosphate isomerase; D002238:Carbohydrate Epimerases; D019747:Aldose-Ketose Isomerases