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

Abstract

Blue crab, Caiinectes sapidus, hemolymph and digestive glands were examined at differentstagesofthe molt cycle to determine whether molting affectedtissue 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 con centrations ofcopper or zinc. Concentrations ofhemocyanin, 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 papershellstage(B1).Zinc followed the same generalpatternin both hemolymph and digestive glands. The cytosolic distributions of copper and zinc were determined in the digestive glands using gel filtrationchromotography.The elution profilesshowed that the percentagesofcopper and zinc on metallothionein rangedfrom 10%copper/ 90%zinc at D1 to 100%copper at B1. The estimated concentrations of metallothi onein were highestduringintermolt (C1)and premolt (D1-D3) and lowest duringthe papershell(B1).The observedchanges in the tissue and cytosolic partitioningof cop per and zinc are consistent with the physiological changes occurring in the crabs. These observations support the hypothesis that metallothioneins are naturally occur ringproteinsthat are actively involved in the synthesis of hemocyanin and zinc regu lation duringthe normal processesof growthin blue crabs.