The interaction of Ibuprofen with Aldehyde dehydrogenase (ALDH) was investigated by fluorescence spectroscopy. Spectrofluorimetric measurements revealed that Ibuprofen could not strongly quench the ALDH intrinsic fluorescence but produced a non-fluorescent complex. ALDH has one binding mode for Ibuprofen at its saturating concentration. The dissociation constant (Kd) value of the ALDH-Ibuprofen complex was 2.20 X 10-5 M with an association constant (Ka) of 1.54 X 10-8 M at 25?C, pH 7.0 indicating ALDH-Ibuprofen complex dissociation is more favourable than its association. The equilibrium constant of ALDH-Ibuprofen complex was not significantly affected by acidic pH of 5.0 and alkaline pH 9.0. The standard Gibbs free energy changes (ΔG) of dissociation of ALDH-Ibuprofen complex were not spontaneous but entropic driven. The thermodynamic data showed that the interaction between ALDH and Ibuprofen was through Van der Waals forces and Hydrogen bond. Speculatively, the affinity of Ibuprofen for ALDH could be used as a structural probe to examine the inhibitory mechanism for treatment of ALDH associated diseases.
Keywords: Ibuprofen; Aldehyde dehydrogenase; fluorescence quenching, Association constant
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