INTERACTIONS OF VARIOUS SKELETAL INTRACRYSTALLINE COMPONENTS WITH CALCITE CRYSTALS

The calcitic skeletal elements of many organisms contain small amounts of proteins and glycoproteins which are incorporated within single cr ystals of calcite. Extraction and partial purification of the intracry stalline macromolecules allowed the identification of their interactio ns with synthetic calcite crystals. Specific interactions were inferre d from induced morphological modifications associated with the develop ment of new faces on calcite crystals grown in the presence of these m acromolecules in solution. Partially purified macromolecules extracted from within sea urchin spines interacted only with faces roughly para llel to the c crystallographic axis of calcite, producing well-develop ed (01l} faces. Macromolecules extracted from within mollusk shell pri sms separated into two fractions each having a characteristic amino ac id composition and displayed distinct specific interactions with growi ng calcite crystals: A highly acidic fraction interacts with the {001} set of faces, while a different fraction, which is only moderately ac idic and has an amino acid composition similar to that of the sea urch in spines, interacts specifically with the {01l} set of faces. Magnesi um, a major ionic component of the sea urchin spines, causes the devel opment of the {011} set of crystal faces. The existing knowledge on th e direction of intercalation of the macromolecules in the biogenic cry stals agrees with the interacting planes in the synthetic crystals, su ggesting the relevance of our in vitro assay to the system in vivo. We suggest that each separate mode of interaction may infer a specific r ole in the regulation of biological crystal growth.