FLUORESCENCE QUENCHING IN RIBOFLAVIN-BINDING PROTEIN AND ITS COMPLEX WITH RIBOFLAVIN

Fluorescence quenching of tryptophan residues in egg-white riboflavin- binding protein by two typical quenchers (charged iodide and uncharged acrylamide) reveals acid-induced changes of protein conformation. At neutral pH, acrylamide flow in macromolecule, (i.e., the quenching eff ect) is decisive; tryptophan residue accessibility for iodide is small . At low pH, some tryptophan residues are exposed to the protein surfa ce and become more accessible to iodide. In contrast, acrylamide is le ss able to permeate this conformational state of RBP. Fluorescence of tryptophan residues in riboflavin-RBP complex and chemically N-bromosu cinimide-modified RBP was quenched by iodide and acrylamide.