Molecular Pharmacology, Vol 20, 138-144, Copyright © 1981 by the American Society for Pharmacology and Experimental Therapeutics

Interaction of Insecticides with Human Serum Albumin

¹ Toxicology Program, Department of Entomology, North Carolina State University, Raleigh, North Carolina 27650

The binding of chlorinated hydrocarbon, carbamate, and organophosphate insecticides to human serum albumin was studied at pH 7.0 and 16 and 26° using equilibrium dialysis, difference spectra, and fluorescence. There is one site of higher affinity than the other sites and 4-6 binding sites of moderate affinity. The affinity is inversely related to the aqueous solubiity of the compounds. The interaction is primarily hydrophobic as binding is only weakly temperature dependent. Binding gives rise to a long wavelength shift of the tyrosyl and tryptophyl absorption spectra. The protein fluorescence is quenched to varying degrees as a result of the binding. The difference spectra and fluorescence quenching indicate that tyrosine and tryptophan residues are located close to the moderate affinity binding sites, although the possible role of binding-induced conformational changes cannot be ruled out. A red shift in the spectrum of bound carbaryl and carbofuran, and a severalfold decrease in binding in F form as compared to that in N form for most of the insecticides, suggests that the binding sites are in the regions which are formed by interactions between hydrophobic surfaces of several domains of albumin.

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ACKNOWLEDGMENT The authors gratefully acknowledge the aid of Dr. R. J. Monroe in statistical analysis of the data.