Interactions of atrazine and 2,4-D with human serum albumin studied by geland capillary electrophoresis, and FTIR spectroscopy

The herbicides 6-chloro-N-ethyl-N '-(1-methylethyl)-1,3,5-triazine-2.4-diam ine (atrazine) and 2,4-dichlorophenoxyacetic acid (2,4-D) are widely used i n agricultural practice to fight dicotyledon weeds mainly in maize, cereals , and lucerne. As a result, these compounds are found not only in the plant s. soil, and water, but also in the cultivated ground in the following year s as well as in agricultural products such as fruits, milk, butter, and sug ar beet. The toxicological effects of herbicides occur in vivo, when transp orted to the target organ through the bloodstream. It has been suggested th at human serum albumin (HSA) serves as a carrier protein to transport 2,4-D to molecular targets. This study was designed to examine the interaction o f atrazine and 2,4-D with HSA in aqueous solution at physiological pH with herbicide concentrations of 0.0001-1 mM, and final protein concentration of 1% w/v. Gel and capillary electrophoresis. UV-visible and Fourier transfor m infrared spectroscopic methods were used to determine the drug binding mo de, the drug binding constant, and the protein secondary structure in aqueo us solution. Structural analysis showed that different types of herbicide-H SA complexes are formed with stoichiometric ratios (drug/protein) of 3:1 an d 11:1 for atrazine and 4.5:1 and 10:1 for 2,4-D complexes. Atrazine showed a weak binding affinity (K = 3.50 x 10(4) M-1), whereas two bindings (K-1 = 2,50 x 10(4) M-1 and K-2 = 8.0 x 10(3) M-1)were observed for 2,4-D comple xes. The herbicide binding results in major protein secondary structural ch anges from that of the alpha -helix 55% to 45-39% and beta -sheet 22% to 24 -32%, beta -anti 12% to 10-22% and turn 11% to 12-15%, in the drug-HSA comp lexes. The observed spectral changes indicate a partial unfolding of the pr otein structure, in the presence of herbicides in aqueous solution. (C) 200 1 Published by Elsevier Science B.V.