The orientation of apatite crystals in Lingula unguis shell.

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The orientation of apatite crystals, which compose the Lingula <I>unguis</I> shell, was investigated by means of X-ray diffraction and scanning electron microscopy. The c-axis of apatite is almost parallel to the shell surface and is almost perpendicular to the growth line, except on the central stria where the c-axis is almost parallel to the growth line. The degree of orientation is high in the lateral margin and the inner surface and is slightly low in the central part and in the outer-surface. The texture of the fractured shell reflects the orientation of the apatite crystals. The overall composition of amino acid is analyzed for several parts of shell. The most superior amino acid in amount is alanine (about 1/3) and following it are glycine (about 1/7), asparagin acid, arginine, and glutamine. Small amounts of hydroxyproline and hydroxylysine are also present. This suggests that collagen-like protein is contained in the shell. The amino acid composition varies somewhat in relation the position. The content of glycine, proline, hydroxyproline, and hydroxylysine are highest and that of alanine is lowest in the outer layer near the apex.
歯科基礎医学会の論文