Fluorescence properties of o-aminobenzoyl-labeled proteins.

Isatoic anhydride reacts with nucleophile groups of proteins to yield o-aminobenzoyl protein conjugates. The fluorescence emitted by the chromophore decays in a multiexponential manner with average fluorescence lifetimes ranging from 9.9 to 10.7 ns. The steady emission anisotropy, measured upon excitation at 330 nm, is influenced by the molecular mass of the protein to which o-aminobenzoyl is attached. The fluorescence properties of o-aminobenzoyl are suitable for rotational correlation time measurements of proteins smaller than 65 kDa. The technique of emission anisotropy can be used to detect interactions between proteins in solution, provided one of the proteins is labeled with o-aminobenzoyl.