S- (Pyridin-2-ylthio) -L-homocysteine

(S) -2-amino-4- (2- (pyridin-2-yl) disulfanyl) butanoic acid is a small molecule reagent with a 2-thiopyridine linked to a short amino acid. SPDP is a thiol-specific labeling reagent, commonly used in reversibly binding cysteine residues on proteins. The disulfide bond it forms with the cysteine is selectively cleaved in the reducing environment of the cell cytoplasm.