The “Hidden Ligand” of the Galactose‐Binding Protein

Following tryptophan fluorescence of the galactose‐Binding Protein during dissociation of the ligand it has been found that glucose dissociates with a half life of less than 5 s. Similarly, fast dissociation was also observed by following release of radioactively labelled glucose from Sepharose‐coupled galactose‐binding protein upon dilution. Accordingly, a previous claim that the galactose‐binding protein contains glucose as a non‐dissociable “hidden ligand” [G. Richarme and A. Kepes (1974) Eur. J. Biochem. 45, 127–133] has to be reinterpreted.