10:00 AM - 10:15 AM
[BPT03-05] Relation between the organic network and the crystal defects in the calcite of the prismatic layer of Pinctada fucata
Keywords:biomineral, shell, chitinase
To reveal the components of the organic networks and formation mechanism of the small angle grain boundaries in the calcite crystal of the prismatic layer, we extracted the organic network from the prismatic layer and tried to identify the components. The IR spectrum of acetic acid-insoluble materials from the prisms revealed that the major component of the organic network was chitin. LC-MS/MS analysis of acetic acid-insoluble and SDS/DTT-soluble fractions showed that the chitinolytic enzymes such as chitinase and chitobiase were involved in the intracrystalline organic matrices of the prismatic layer. These results suggested that the chitinase and chitobiase regulate the formation of chin fibers that interact with the calcium carbonate to make the small-angle grain boundaries. To understand the function of the chitinolytic enzymes in the prismatic layer, calcium carbonate was precipitated in the chitin hydrogel after being treated with the commercially available enzyme. The calcite crystals precipitated in the chitin hydrogel appeared to contained larger crystal defects as the chitinolytic enzyme concentration increase and crystal defects similar to those in the prismatic layer were observed as to some extent concentration. In addition to observation, a variance of lattice spacing was calculated from peak broadening in powder X-ray diffraction and compared among the these calcite crystals. As a result, a variance lattice spacing tended to increase depending on chtinolytic enzyme concentration, implying that chitinolytic enzyme decrease the thickness of the chitin fiber to increase the interaction between chitin fibers and calcium carbonate. Such interaction is probably important to produce the small-angle grain boundaries in the calcite crystal and strengthens the toughness of shell.