Silva Dílson, Cortez Célia M, Cunha-Bastos Jayme, Louro Sônia R W
Department of Physiology, Rio de Janeiro State University, 1 Rua Prof. Manuel de Abreu, 444-5 andar, 20550-170, Rio de Janeiro, Brazil
Toxicol Lett. 2004 Feb 28;147(1):53-61. doi: 10.1016/j.toxlet.2003.10.014.
Methyl parathion (MP; O,O-dimethyl O-p-nitrophenyl phosphorothioate) is an organophosphorous compound still largely used in agriculture and fish hatcheries. This pesticide is not quite selective and is potentially toxic for both vertebrates and invertebrates. Its mechanism of acute toxicity is the inhibition of the enzyme acetylcholinesterase in nervous tissue. Binding of pesticides to plasma proteins is one of many factors that influence their distribution and elimination. The free concentration available for toxic action can be effectively reduced for pesticides with high binding to plasma proteins, although the affinity of pesticides to plasma proteins is often lower than for the enzyme targets. Several different transport proteins exist in blood plasma, but albumin only is able to bind a wide diversity of xenobiotics reversibly with high affinity. It was already known that parathion (ethyl parathion) exhibits a high affinity to human and bovine serum albumins. We studied interactions of methyl parathion with these albumins by using fluorescence quenching techniques. We selectively excited the fluorescence of tryptophan residues with a 290 nm wavelength light, and observed quenching by titrating human and bovine serum albumin solutions with methyl parathion. Stern-Volmer graphs were plotted and quenching constants were estimated. Our results pointed to the formation of complexes of methyl parathion with albumins. Association constants at 25 degrees C were 3.07 x 10(4) (1.2 x 10(3))M(-1) for human serum albumin, and 1.96 x 10(4) (+/- 4.5 x 10(2))M(-1) for bovine serum albumin. At 37 degrees C, they were 1.08 x 10(4) (+/- 2.0 x 10(2))M(-1) for human serum albumin, and 8.16 x 10(3) (+/- 1.9 x 10(2))M(-1) for bovine serum albumin. Results also suggest that the primary binding site for methyl parathion on albumin is close to tryptophan residues 214 of human serum albumin and 212 of bovine serum albumin.
甲基对硫磷（MP；O，O-二甲基-O-对硝基苯基硫代磷酸酯）是一种有机磷化合物，仍广泛应用于农业和鱼苗孵化场。这种杀虫剂选择性不强，对脊椎动物和无脊椎动物都有潜在毒性。其急性毒性机制是抑制神经组织中的乙酰胆碱酯酶。农药与血浆蛋白的结合是影响其分布和消除的众多因素之一。对于与血浆蛋白结合力高的农药，可有效降低其产生毒性作用的游离浓度，尽管农药与血浆蛋白的亲和力通常低于与酶靶点的亲和力。血浆中存在几种不同的转运蛋白，但只有白蛋白能够以高亲和力可逆地结合多种外源性物质。人们已经知道对硫磷（乙基对硫磷）对人血清白蛋白和牛血清白蛋白具有高亲和力。我们使用荧光猝灭技术研究了甲基对硫磷与这些白蛋白的相互作用。我们用波长290nm的光选择性激发色氨酸残基的荧光，并通过用甲基对硫磷滴定人血清白蛋白和牛血清白蛋白溶液来观察猝灭现象。绘制了斯特恩-沃尔默图并估算了猝灭常数。我们的结果表明甲基对硫磷与白蛋白形成了复合物。25℃时人血清白蛋白的缔合常数为$3.07×10^4(1.2×10^3)M^{-1}$，牛血清白蛋白的缔合常数为$1.96×10^4(±4.5×10^2)M^{-1}$。在37℃时，人血清白蛋白的缔合常数为$1.08×10^4(±2.0×10^2)M^{-1}$，牛血清白蛋白的缔合常数为$8.16×10^3(±1.9×10^2)M^{-1}$。结果还表明，甲基对硫磷在白蛋白上的主要结合位点靠近人血清白蛋白的色氨酸残基214和牛血清白蛋白的色氨酸残基212。
