8-Fluoro-8-demethylriboflavin as a 19F-probe for flavin-protein interaction. A 19F NMR study with egg white riboflavin binding protein.

Binding of 8-fluoro-8-demethylriboflavin to riboflavin binding protein was studied 19F-NMR spectroscopically. The pH dependence of 19F chemical shift of this fluoro derivative both free and bound to the protein revealed a shift of pKa associated with N(3)-H to alkali when bound to the protein. 19F chemical shift of the fluoro derivative bound to the protein is in a higher magnetic field than that of the free derivative in the neutral to acidic pH region. These results are interpreted in terms of the environmental changes at the 8- and 3-positions of isoalloxazine, indicating the applicability of this derivative for probing flavin-protein interaction at these positions.