5-FTSC reacts with ketones to yield relatively stable hydrazones and with aldehydes to yield hydrazones that are somewhat less stable, though they may be formed faster (compared to ketones). These hydrazones are generally reduced with sodium borohydride (NaBH4) to further increase the stability of the linkage. 5-FTSC has been used to make a wide variety of biomolecules such as L-aspartase-a-decarboxylase, enzyme-oxidized live plant protoplasts, immunoglobulins, thrombin and antithrombin.
Ahn B, et al. (1987). Use of fluorescein hydrazide and fluorescein thiosemicarbazide reagents for the fluorometric determination of protein carbonyl groups and for the detection of oxidized protein on polyacrylamide gels. Anal Biochem 161, 245-57; Atha DH, et al. (1984). Interaction and thermal stability of fluorescent labeled derivatives of thrombin and antithrombin III. Biochim Biophys Acta 785, 1-6.