Interaction of pendimethalin (PM) herbicide with the major transporter in human circulation, human serum albumin (HSA), was studied using fluorescence, circular dichroism (CD), and molecular modeling methods. The attenuation of the fluorescence intensity of HSA in the presence of PM revealed formation of the PM-HSA complex. Analysis of the fluorescence quenching data showed moderately strong binding affinity between PM and HSA. Both hydrophobic interactions and hydrogen bonding were suggested to stabilize the PM-HSA complex, based on thermodynamic data. Binding of PM to HSA induced perturbation in the microenvironment around the aromatic fluorophores as well as secondary and tertiary structural changes in the protein. Complexation of PM with HSA led to an increase in its thermal stability. Both site marker displacement and molecular modeling results suggested site I, located in subdomain IIA as the preferred binding site of PM on HSA.

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Background To investigate the interaction of pendimethalin (PM), a commonly used herbicide, with various mammalian serum albumins. Methods The interactions of PM with serum albumins of bovine (BSA), sheep (SSA), porcine (PSA) and rabbit (RbSA) were studied using fluorescence quenching titration and site marker displacement experiments. Results A comparison of the PM-induced quenching of the fluorescence of these albumins with that published for human serum albumin (HSA) showed similarity between BSA and HSA. The PM binding affinity of these albumins was found to follow the order: SSA>BSA>RbSA>PSA. Warfarin (WFN) displacement results also suggested similar displacing action of PM on WFN-BSA complex, when compared to the published results on WFN-HSA complex. Conclusion The results suggested close similarity between BSA and HSA in terms of PM binding characteristics and hence bovine can be selected as a suitable animal model for further toxicological studies of PM.

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