Lead-binding by ceruloplasmin

Abstract

Many metal-binding proteins have been reported in human serum, and Mangkalee (1994) reported transferrin, Tf, the iron transporting protein, could bind to Pb. It is the aim of this study to prove that ceruloplasmin (Cp, Cu-binding protein) could also serve as another Pb-carrier. When human serum was incubated with 1.8 mg/l lead acetate and the protein-bound metal was quantitated with atomic absorption spectrophotometer, it was found that bound Pb increased by 0.12 ppm while Cu was released. The oxidase activity of serum decreased concomitantly with Pb binding. This suggested that ceruloplasmin, the physiological Cu transporting protein, was one of lead-binding factor(s) in human serum. The finding was confirmed with Sephadex G-200 column chromatography and polyacrylamide gel electrophoresis of Pb-treated human serum. Optimum pH for metal-binding on ceruloplasmin was pH 6.0. The binding of Pb decreased by 3.16% when Cp was stored at 4°c for 3 days. Confirmation with purified Cp showed that Pb binding, Cu released and the decrease of oxidase activity were concentration dependent and corresponded very well with each other. The metal-chelators namely, 100 mg/ml CaNa2EDTA, 100 mg/ml Dimercaprol and 1,000 mg/ml Penicillamine could reduce the concentration of Pb bound on Cp molecules by 89.1, 96.5 and 99.0 %, respectively. However, the Pb-binding Cp and Pb-freed Cp (with metal-chelators) could not be fractionated with IEF-PAGE at pH 4.0-6.0.