Frequency domain fluorescence studies of yeast phosphoglycerate kinase and its ternary complex.

A frequency domain fluorescence study of yeast phosphoglycerate kinase has been performed to observe the effect of substrates on the structure and dynamics of the enzyme. At 20 degrees C and pH 7.2, a biexponential decay is observed for tryptophanyl emission. The short fluorescence lifetime (0.4 ns) component is associated with a spectrum having a 329-nm maximum and a 18.4-kJ/mol activation energy, Ea, for thermal quenching. The long-lifetime (3.5 ns) component has a 338-nm maximum and an Ea of only 7.9 kJ/mol. Tentatively we assign the short and long-lifetime components to Trp-333 and Trp-308. Binding of the substrates ATP and 3-phosphoglycerate leads to a significant increase in the fluorescence lifetime, the red shift of the emission spectrum and in the decrease in the Ea for both components. Acrylamide-quenching studies indicate that the two tryptophan residues have about the same degree of kinetic exposure to the quencher and that the binding of the substrates causes a very slight change in the quenching pattern. These fluorescence studies indicate that the binding of the substrates to phosphoglycerate kinase may influence the conformational dynamics around the two tryptophan residues located on one of the protein's domains.