Phosphorescence of Pyridoxal Kinase at Room Temperature: The Effects of Ligands Bound to the Nucleotide Site

Summary

Ligands bound to the nucelotide site of pyridoxal kinase influence the phosphorescence properties of tryptophanyl residues. Binding to the substrate ATP perturbs the triplet state of the protein leading to a significant decrease in phosphorescence lifetime from 0.9 to 0.3ms. The effect is attributed to changes in the flexibility of the embedding macromolecular matrix elicited by binding of the substrate. The probe DANS-GABA inhibits the enzyme by displacing ATP from the nucleotide binding site and quenches protein phosphorescence by a mechanism of triplet-singlet energy transfer. Ligand bonds to specific sites on proteins are suitable to study specific quenching mechanisms leading to deactivation of the triplet state at room temperature.