A Polarity‐Sensitive Fluorescent Amino Acid and Peptide for the Ratiometric Detection of Biomolecule Interactions

: A fluorescent amino acid containing our recently developed 1,5-naphthyridin-2(1H)-one based- fluorophore, which is a structural component of the fluorescent natural compounds amarastelline A and nigakinone, has been developed. It has useful functions, that is, solvent-polarity-dependent change of fluorescence ratio at 370/480 nm and strong fluorescence in both aqueous solution and less polar organic solvents. To demonstrate its utility, it was incorporated into a C5 peptide with the aim of detecting the interaction of this peptide with calmodulin. As expected, the fluorescence ratio at 370/480 nm of the peptide was changed by the calmodulin only in the presence of Ca2+ , thus indicating that the fluorescent peptide could sense the conformational change of calmodulin induced by Ca2+ , followed by its interaction. These results also suggest that this fluorescent amino acid as well as its precursor, a succinimidyl ester, could be applicable for detecting various biomolecular interactions.