IDENTIFICATION OF EXTRACELLULAR HEMOGLOBIN AS THE MAJOR HIGH-MOLECULAR-WEIGHT CADMIUM-BINDING PROTEIN OF THE POLYCHAETE ANNELID NEREIS-DIVERSICOLOR

1. A high molecular weight cadmium-binding protein called MP I was iso lated from Nereis diversicolor exposed to 20 ppm of cadmium (CdCl2) fo r 4 days via sea water. 2. The protein had a molecular weight comprisi ng between 20 x 10(6) and 1.5 x 10(6) Da. It shows high absorptions at 280 and 415 nm and contained iron in addition to cadmium. 3. Two dime nsional SDS-PAGE of unreduced and reduced MP I revealed a dissociation pattern similar to that of extracellular haemoglobins of polychaetes and oligochaetes. 4. Furthermore, negatively stained MP I molecules ex amined by conventional transmission electron microscopy showed the com mon appearance of extracellular haemoglobins of annelids, 5. Evidence of the extracellular haemoglobin nature for the MP I was found by the identical chromatographic behaviour of MP I with the main Nereis blood component and, by the labelling of blood vessel content with Cd-109 v isualized by autoradiography on paraffin-embedded sections of exposed Nereis.