HEMOCYANIN AND THE BINDING OF CADMIUM AND ZINC IN THE HEMOLYMPH OF THE SHORE CRAB CARCINUS-MAENAS (L)

The trace metals cadmium and zinc are taken up from solution into haem olymph of the shore crab, Carcinus maenas, where they bind to the resp iratory pigment haemocyanin. Investigations using FPLC and PAGE to sep arate the constituent dodecamer and hexamer aggregations of haemocyani n showed a difference between the distribution of cadmium and zinc bet ween the two aggregate states. In the haemolymph, labelled cadmium bin ds not only to haemocyanin but, at least initially, it is also associa ted with low molecular size material or exists as free cadmium ions. T he binding of cadmium to haemocyanin is not an immediate process. Init ially the binding of cadmium favours the hexamer; only later is a more even distribution between the two aggregate states apparent. Newly ta ken up labelled zinc is rapidly bound to haemocyanin. The majority of both total and labelled zinc in the haemolymph is bound to haemocyanin , with the hexamer having a greater binding affinity for zinc than the dodecamer. This suggests that formation of the dodecamer leads to a b locking of zinc-binding sites and/or that the hexamer consists of subu nits which possess a relatively high affinity for zinc. (C) 1998 Elsev ier Science B.V.