Interactions of PCBs with human serum albumin: in vitro spectroscopic study

Following absorption, polychlorinated biphenyls (PCBs) bind to albumin and are transported via blood into the target tissues. PCBs then accumulate in tissues and induce a variety of harmful chronic and developmental effects. The aim of the present study is to determine binding parameters, such as binding constant, quenching constant, and number of binding sites for three PCB congeners (PCB118, PCB126 and PCB153) in complex with human serum albumin (HSA). The binding parameters for the complexes of HSA-PCB118, HSA-PCB126, and HSA-PCB153 excited at 280 nm were compared with those excited at 295 nm. Quenching (static and dynamic) of HSA fluorescence was analyzed based on the Stern-Volmer method. Binding (Ka) constants were calculated according to the Scatchard method and analysis of non-linear regression was based on a two-component model with the Lavenberg-Marquardt algorithm. For all analyzed complexes, a single independent class of binding site for PCB congeners was found in HSA subdomain IIA. Tyrosine residues appear to play the most prominent role in binding of PCB126 to HSA, while tryptophan-214 played a dominant role in interactions of PCB153 with HSA. Among studied PCB congeners, PCB118 formed the most stable complexes with HSA. These results illustrate the importance of studies targeting the binding of PCBs to serum albumin as part of the strategy to understand and protect against toxicity of these environmental toxicants.