Suberoylanilide hydroxamic acid (SAHA) is a class I and class II histone deacetylase (HDAC) inhibitor that binds directly to the catalytic site of the enzyme thereby blocking substrate access. [1] coumarin-Suberoylanilide hydroxamic acid (c-SAHA) is a SAHA derivative where the anilino "cap" group is replaced by 7-amino-4-methylcoumarin to produce a fluorescent probe that competitively binds HDAC. [2] The fluorescence excitation and emission maxima of free c-SAHA is 325 and 400 nm, respectively and is quenched by 50% when bound to HDAC8. [2] This probe can be used to determine binding affinities and dissociation off-rates of HDAC enzyme-inhibitor complexes and is well-suited for high-throughput screening.

Reference:
[1]. Marks, P.A., and Breslow, R. Dimethyl sulfoxide to vorinostat: Development of this histone deacetylase inhibitor as an anticancer drug. Nat. Biotechnol. 25(1), 84-90 (2007).
[2]. Singh, R.K., Mandal, T., Balasubramanian, N., et al. Coumarin-suberoylanilide hydroxamic acid as a fluorescent probe for determining binding affinities and off-rates of histone deacetylase inhibitors. Anal. Biochem. 408(2), 309-315 (2011).