Truncated green fluorescent protein (GFP) that is refolded after removing the 10th beta-strand can readily bind to a synthetic strand to recover the absorbance and fluorescence of the whole protein. This allows rigorous experimental determination of thermodynamic and kinetic parameters of the split system including the equilibrium constant and the association/dissociation rates, which enables residue-specific analysis of peptide protein interactions. The dissociation rate of the noncovalently bound strand is observed by strand exchange that is accompanied by a color change, and surprisingly, the rate is greatly enhanced by light irradiation. This peptide protein photo-dissociation is a very unusual phenomenon and can potentially be useful for introducing spatially and temporally well-defined perturbations to biological systems as a genetically encoded caged protein.