Cadmium transport in blood serum

Abstract

The binding of Cd2+to human serum transferrin in 0.1 M N-(2-hydroxyethyl) piperazine-N′-2-ethanesulfonic acid and 5 mM sodium bicarbonate at pH 7.4 has been studied by difference ultraviolet spectrophotometry. The apparent association constants were found to be 2.61 × 105M—1and 8.51 × 104M— 1, respectively. These association constants are pH-dependent, reducing with both increasing and decreasing pH. The apparent pKavalues were found to be 4.93 and 5.42. Competitive assays of binding of Cd2+to transferrin in the presence of citrate and human serum albumin at molar ratios corresponding to those found in normal plasma showed that a considerable amount of Cd2+was not bound to transferrin. The competitive binding assays indicate that ∼50% of Cd2+is bound to transferrin, ∼37% to albumin and reminder to citrate. These results therefore suggest that, although transferrin at pH 7.4 is the major Cd2+-binding component of plasma, an appreciable amount of Cd2+may be bound to albumin.