ALTERATION OF THE INTRAMOLECULAR DYNAMICS OF GLYCOGEN-PHOSPHORYLASE-BBY ALLOSTERIC LIGANDS

Phosphorylase b (E.C.2.4.1.1), prepared from rabbit skeletal muscle, w as used to study whether the binding of allosteric ligands modifies th e intramolecular dynamics of the protein matrix, Protein dynamics were monitored through the fluorescence and phosphorescence parameters of the 12 tryptophan (Trp) residues (one monomer) of thr enzyme. The Phos phorescence lifetime was measured at room temperature both in the abse nce and the presence of ligands. The addition of an allosteric inhibit or (ATP) decreased the lifetime, while the presence of activator (AMP) and/or substrate (G-1-P) had no detectable effect. The lifetime data allow us to conclude that the environment of the buried tryptophans be comes more flexible upon the binding of ATP, while the other Ligands d id not induce such change. The ATP induced perturbation was also exami ned by the quenching of Trp fluorescence by acrylamide, The quenching parameters did not show any change, suggesting that the effect of ATP is localized to the vicinity of the phosphorescent Trp residues. (C) 1 998 Elsevier Science S.A.