A comparison of calcium binding in Callinectes sapidus premolt and postmolt cuticle homogenates: implications for regulation of biomineralization.

Cuticle tissue homogenates (CTHs) from Callinectes sapidus premolt cuticle bound approximately 367% more Ca2+ ions than did those from the postmolt cuticle. The pH-stat assay which was used to compare in vitro CaCO3 nucleation times confirmed that the premolt CTHs had greater inhibitory activity than did the postmolt CTHs. This inhibitory activity was indicated by CaCO3 nucleation times in excess of control values. Premolt nucleation times exceeded those of postmolt samples by approximately 340%. A positive correlation was observed between Ca2+ binding and calcification inhibitory activity for both premolt and postmolt CTHs. Heat pretreatment of CTHs at 70 degrees C for a 24-hr period had no significant effect on their Ca2+ binding. However, this heat pretreatment decreased their calcification inhibitory activity. Pretreatment of CTHs with Ca2+ diminished their calcification inhibitory activity. These results are consistent with a mechanism for inhibition of biocalcification by these proteins which involves their initial reversible binding to nascent calcite nuclei growth steps and kinks, rather than their in vivo interaction with free Ca2+ ions in solution.