Cadmium-binding to transferrin in the plasma of the common carp Cyprinus carpio

In this study, it was investigated by autoradiography with radioactive cadm ium after Western blotting of two-dimensional electrophoresis gels, to whic h proteins cadmium is mainly bound in plasma of common carp Cyprinus carpio . The obtained results demonstrate that in carp plasma, cadmium is primaril y bound to two high molecular weight proteins. Relative small amounts are b ound to a protein with M-r similar to 60 000. The other metal-binding prote in, with M-r similar to 70 000 and pI similar to 6.7 was identified as tran sferrin. The conditional equilibrium constants for the binding of cadmium i ons to the two metal-binding sites of this protein were calculated as log K -1 = 5.40 +/- 0.12 and log K-2 = 4.66 +/- 0.21, which are comparable to tho se of human transferrin under the same experimental conditions. Transport o f cadmium in plasma of carp was found to be different from that of brown tr out Salmo trutta and man, where cadmium is mainly bound to albumin and tran sferrin. The prominent binding of cadmium to transferrin can be explained b y the absence or at least the very low concentrations in which albumin is p resent in carp plasma. (C) 2001 Elsevier Science Inc. All rights reserved.