Regulation of Carbonate Calcification by Organic Matrix

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Abstract
The organic matrix of calcium carbonate structures can be involved in the formation of the biomineral by regulating various stages of crystal growth. The preponderance of evidence suggests that matrix can act as an initiator of crystal growth at the mineralizing front. The mechanism for this initiation is not known. However, the matrix may provide a template for the crystal lattice, or more likely, a surface that can simply stabilize the critical nucleus of calcium and carbonate. The degree of specialization of the nucleation sites is uncertain; however, they are hypothesized to be a class of soluble, acidic, calcium-binding polymers which are present in matrix extracted from biomineral. Recent studies have revealed that similar soluble components of extracted matrix have the capability of inhibiting nucleation and crystal growth in vitro and biomineralization in organisms exposed to the extracts. Further, crystals grown in vitro in the presence of extracted matrix have a morphology distinct from those of crystals grown without matrix. These findings generally support the hypotheses generated either a priori or from morphological observations which suggest that matrix must limit crystal growth and may well influence structure of biomineral. Hypotheses which explain a dual function of the soluble matrix have these components periodically released to the mineralization front where they can associate with more insoluble forms of matrix and sequentially initiate or inhibit growth. There also exists evidence to suggest that soluble regulatory components are intra-crystalline in orientation and thus may be released continuously

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