title: Fluorescence decay time measurements of Eu3+-ATP-enzyme complexes. Replacement of the metal hydration water by active site ligands.
abstract: Measurements of the fluorescent lifetimes of the rare earth metal Eu3+ in varying mole fractions of H2O/D2O were used to determine the hydration of the metal in the presence of ATP and/or hexokinase or chloroplast reversible ATPase. The number of water molecules coordinated to the metal in Eu3+-ATP was estimated to be 2.6; when this complex is bound to hexokinase, 1 water molecule is displaced. Upon binding to chloroplast reversible ATPase, the metal coordinates 1 water molecule while the Eu3+-ATP complex does not retain any associated solvent. These numbers are in contrast to the 9 solvent molecules coordinated to the naked metal ion. These results are discussed in reference to mechanistic and structural considerations of the two enzymes.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D002736:Chloroplasts / Q000201:enzymology; D005063:Europium / Q000494:pharmacology*; D006593:Hexokinase / Q000378:metabolism*; D007700:Kinetics; D010944:Plants / Q000201:enzymology; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013050:Spectrometry, Fluorescence
chemical_list: D005063:Europium; D000255:Adenosine Triphosphate; D006593:Hexokinase; D000251:Adenosine Triphosphatases