METAL REGULATION AND MOLTING IN THE BLUE CRAB, CALLINECTES SAPIDUS: COPPER, ZINC, AND METALLOTHIONEIN

¹ National Marine Fisheries Service, NOAA, Southeast Fisheries Center, Beaufort Laboratory, Beaufort, North Carolina 28516

Blue crab, Callinectes sapidus, hemolymph and digestive glands were examined at different stages of the molt cycle to determine whether molting affected tissue and cytosolic partitioning of copper and zinc and, if so, whether metallothionein was involved. The crabs used in these determinations were not exposed to elevated concentrations of copper or zinc. Concentrations of hemocyanin, copper, and zinc in the hemolymph all decreased significantly during molt. They were lowest at the soft crab stage (A₂) and highest during premolt(D₁-D₃) and intermolt(C₄). The digestive gland copper concentrations also were highest during premolt (D₁-D₃) and lowest in the papershell stage (B₁). Zinc followed the same general pattern in both hemolymph and digestive glands. The cytosolic distributions of copper and zinc were determined in the digestive glands using gel filtration chromotography. The elution profiles showed that the percentages of copper and zinc on metallothionein ranged from 10% copper/90% zinc at D₁ to 100% copper at B₁. The estimated concentrations of metallothionein were highest during intermolt (C₁) and premolt (D₁-D₃) and lowest during the papershell (B₁). The observed changes in the tissue and cytosolic partitioning of copper and zinc are consistent with the physiological changes occurring in the crabs. These observations support the hypothesis that metallothioneins are naturally occurring proteins that are actively involved in the synthesis of hemocyanin and zinc regulation during the normal processes of growth in blue crabs.