Promotion and Inhibition of Calcium Carbonate Crystallization In Vitro by Matrix Protein From Blue Crab Exoskeleton

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Abstract
Soluble organic matrix isolated from dorsal carapaces of the blue crab, Callinectes sapidus, inhibited CaCO3 crystallization when free in solution. Immobilized matrix complexes, prepared by crosslinking soluble matrix to decalcified crab carapace, promoted CaCO3 formation in that crystallization in the presence of the immobilized soluble matrix complexes began sooner than in solution controls. In the experimental treatments, deposition of crystals occurred only within the complexes and not in the crystallization solutions. Chitin, a polymer of N-acetyl-D-glucosamine, and chitosan, a deacetylated chitin, which are both insoluble products of the organic matrix of the crab carapace containing little to no matrix protein, did not promote CaCO3 crystallization. Complexes of immobilized polyanionic synthetic peptides on chitosan also promoted CaCO3 crystallization. Addition of a hydrophobic tail (Ala8) to the polyanionic peptide (Asp20) reduced the rate of promotion, possibly because the hydrophobic tail formed a diffusion barrier around crystal nuclei growth sites, suppressing interactions of nascent crystal nuclei with ions in the bulk solution.