Thiolation through disulfide reduction

Thus, this reagent can be used to label fluorescently proteins and other biomolecules containing free sulfhydryl residues. If there are no —SH groups available, their creation can be accomplished by reduction of indigenous disulfides or through the use of various thiolation reagents (Chapter 1, Section 4.1). 

Figure 21.5 SPDP can be used to modify both an antibody and a toxin molecule for conjugation purposes. In this case, the antibody is thiolated to contain a sulfhydryl group by modification with SPDP followed by reduction with DTT. A toxin molecule is then activated with SPDP and reacted with the thiolated antibody to effect the final conjugate through a disulfide bond.

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