Binding of phenthoate to bovine serum albumin and reduced inhibition on acetylcholinesterase

Organophosphorus pesticides (OPs) are of environmental significance due to their high toxicity to animals. Binding to plasma proteins may effective influence the toxicological properties of xenobiotics. In an attempt to evaluate the affinity of phenthoate (PTA) to bovine serum albumin (BSA) and inhibitory ability of bound PTA to acetylcholinesterase (AChE), we investigated the interactions between phenthoate (PTA) and bovine serum albumin (BSA) using tryptophan fluorescence quenching and subsequent inhibition on AChE activity by PTA. The results showed that PTA caused the fluorescence quenching of BSA because of the formation of a PTA–BSA complex. Quenching constants (Ksv), determined using the Sterns–Volmer equation to provide a measure of the binding affinity between PTA and BSA at 303, 306, 310 and 313 K were (3.4295 ± 0.0763) × 10−4, (3.2446 ± 0.0635) × 10−4, (3.0434 ± 0.0856) × 10−4 and (2.8262 ± 0.0569) × 10−4 M−1, respectively. The thermodynamic parameters, ΔH and ΔS were −25.04 kJ mol−1 and 168.94 J mol−1 K−1, respectively, which indicated that the electrostatic interactions played a major role in PTA–BSA association. The presence of BSA consistently reduced the inhibitory ability of PTA on AChE, with the relative activity being increased from 46.98 to 61.71% for the concentration range of BSA between 0 and 4.0 g L−1.