SPDP

Spacer arm 6.6 angstroms. Heterobifunctional crosslinker. Used to introduce protected thiol groups into a variety of proteins. Treatment with DTT releases 2-pyridylthione and mercaptopropionyl modified amine. The thiolated molecule can then be coupled to a second molecule through a halogen acetamide or maleimide group. The thiolated molecule can also be reacted with a second pyridyldisulfide containing molecule. Soluble in DMF.

Carlsson, J., et al. (1978) Protein thiolation and reversible protein-protein conjugation. N-succinimidyl-3-(2-pyridyldithio)propionate, a new heterobifunctional reagent. Biochem. J. 173 , 723-737. 
Cumber, A.J., et al. (1985) Preparation of antibody-toxin conjugates. Meth. Enzymol . , New York : Academic Press, 112, 207-225. 
Engstler, M., et al. (2004) J. Cell Sci.117, 1105-1115. 
Itoh, Y., et al. (2001) Proc. Natl. Acad. Sci. USA98, 4883-4887. 
Wang, D., et al . (1997) Bioconjug. Chem. 8 , 878-884.

Releases a detectable by product when reacted with a free sulfhydryl group; by measuring the release of pyridine-2-thione at 343 nm, the reaction can be easily followed 
Amine reactive Sulfo NHS ester reacts rapidly with any primary amine-containing molecule 
Disulfide bond in the spacer arm is readily cleaved by 10-50 mM DTT or TCEP at pH 8.5 
Spacer arm is also cleaved with 5% 2-mercaptoethanol in SDS PAGE sample loading buffer at 100°C for 5 minutes 
Cleavable crosslinker allows separation of crosslinked products 
SPDP crosslinker is membrane permeable, so crosslinking can be carried out inside the cell