Novel protein inhibits in vitro precipitation of calcium carbonate

Organic molecules both coexist and interact with inorganic crystal lattices in biomineralizing tissues. Mineral precipitation and crystal morphology are tightly regulated by the actions of these molecules. Polyacrylamide gel electrophoresis studies on water soluble extracts from the cuticle of Callinectes sapidus (Atlantic blue crab) reveal the presence, in unmineralized nascent premolt cuticle, of proteins which are absent in the mineralized postmolt cuticle. In the present studies, homogenates from both premolt and postmolt C. sapidus cuticles have been tested for their effect on the in vitro precipitation of calcium carbonate. The role of protein in this process was determined by heat pretreatment and trypsin pretreatment of the cuticle homogenates prior to the precipitation assay. The results from these experiments indicate that proteins, with molecular weights of approximately 75,000 and between 10,000 and 20,000, concentrated in the C. sapidus premolt cuticle, inhibit calcium carbonate precipitation in vitro. The inhibitory activity of these proteins appears to be a result of specific interactions since trypsin, myoglobin, and ovalbumin are not inhibitory. The presence of lower amounts of these inhibitory proteins in C. sapidus postmolt cuticle may be responsible for the subsequent mineralization of this tissue.