A fluorescent-based HPLC assay for quantification of cysteine and cysteamine adducts in Escherichia coli-derived proteins

► A fluorescent-based assay for the quantification of thiol adducts is described. ► E. coli-derived recombinant proteins require refolding for activity. ► Cysteine and cystamine from the redox-couple can generate thiol-protein adducts. ► Released thiols are derivatized and separated by reversed-phase HPLC. ► Quantification of thiol adducts is accomplished by comparison to standard curves.