Abstract
A cleavable photoactivable heterobifunctional reagent, the N-hydroxysuccinimide ester of 1-azido-5-naphthalene sulfonyl S-carboxymethylthiocysteamine (NHS-ANS-CTC), was synthesized and characterized. The reagent was applicable to the group-directed modification of protein ligands, such as an invertebrate lectin and a trypsin inhibitor. The modified ligands bound to rabbit erythrocyte ghosts and trypsin, respectively. Upon exposure to ultraviolet light, the modified ligands reacted with their binding proteins to form cross-linked fluorescent products. The crosslinked fluorescent complexes were readily cleaved by reducing the disulfide bond of the reagent, leaving the fluorescent probe on the binding proteins. The photolabeled binding proteins were analyzed by SDS-polyacrylamide gel electrophoresis. The fluorescence intensity of the fluorescent probe was enhanced by 4 - 8 times to improve sensitivity when the SDS-gel was dehydrated with methanol. This phenomenon was also observed with the proteins labeled with l-dimethylamino-5-naphthalene sulfonyl chloride.
