Mercaptalbumin as a selective cadmium-binding protein in rat serum

Cadmium-binding proteins in blood serum were determined on a gel permeation column by high-performance liquid chromatography-inductively coupled argon plasma-atomic emission spectrometry. Cadmium chloride was administered iv to female rats of the Wistar strain in a single dose of 0.4 mg Cd/kg body wt and the rats were killed 1, 2, 3, 5, 10, 20, and 30 min after the injection. The blood serum was separated on an Asahipak GS-520 column and cadmium concentration in the eluate was monitored continuously along with sulfur, zinc, copper, iron, and phosphorus concentrations. Cadmium was selectively bound to mercaptalbumin and the metal was eliminated from blood serum within 30 min in a biphasic mode. Addition in vitro of cadmium chloride into fresh blood serum revealed that cadmium is bound selectively to mercaptalbumin up to approximately 14 micrograms Cd/ml serum. Excess cadmium in blood serum was found in the lower molecular weight fraction. Nonmercaptalbumin produced by oxidative disulfide bond formation between albumin and glutathione or cysteine was not able to bind cadmium. Sulfur and other element profiles were helpful in characterizing metal-binding proteins.