Abstract
The organic matrix is thought to play an important role in controlling crystal growth during the formation of skeletal hard parts. The structural organization of the matrix macromolecular constituents can provide a key to understanding the nature of the control processes. Although the data are limited, both vertebrate and invertebrate organic matrices appear to be organized according to the same “basic motif,” namely a core of relatively hydrophobic structural macromolecules (usually proteins) and surface layers of acidic proteins and polysaccharides. Analyses of the latter from different invertebrate phyla using reversed phase high performance liquid chromatography, reveal that the same two classes of macromolecules are present in each of the three cases studied, emphasizing the fundamental importance of these components in crystal growth. Substantial information, at the molecular level, on the conformations and orientations of matrix constituents in relation to the mineral crystal lattice, is available only for mollusk shells, and to some extent on vertebrate tooth enamel. In these cases the major matrix constituents are aligned with one or more mineral crystallographic axes. These observations suggest that the matrix performs active, specific roles in crystal growth. Although it is still premature to assess the importance of various basic crystal growth mechanisms, the data available do not preclude the possibility that epitaxial crystal growth is an important factor

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