INTERACTION OF INSECTICIDES WITH HUMAN-SERUM ALBUMIN

The binding of chlorinated hydrocarbon, carbamate and organophosphate insecticides to human serum albumin was studied at pH 7.0 and at 16.degree. and 26.degree. C using equilibrium dialysis, difference spectra and fluorescence. There was 1 site of higher affinity than the other sites and 4-6 binding sites of moderate affinity. The affinity was inversely related to the aqueous solubility of the compounds. The interaction was primarily hydrophobic as binding was only weakly temperature dependent. Binding gave rise to a long wavelength shift of the tyrosyl and tryptophyl absorption spectra. The protein fluorescence was quenched to varying degrees as a result of the binding. The difference spectra and fluorescence quenching indicated that Tyr and Trp residues were located close to the moderate affinity binding sites, although the possible role of binding-induced conformational changes could not 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, suggested that the binding sites were in the regions formed by interactions between hydrophobic surfaces of several domains of albumin.