Oyster Shell Protein and Atomic Force Microscopy of Oyster Shell Folia

The organic layers within biominerals often are viewed as sheets that may function in part to limit and define the underlying crystal structure, as well as to promote formation of the next mineral layer. Some insights into the nature of the sheets were revealed by atomic force microscopy (AFM) of surfaces of freshly cleaved fragments of oyster shell folia. Visible in the micrographs were arrays of globular structures that resembled the globules seen in isolated oyster shell protein bound to calcite, mica, and glass. The results of chemical treatment showed that the foliar globules slowly dissolved in 5.25% NaOCl or 1 N NaOH, reacted with an antibody prepared against an isolated oyster shell protein, and were hydrolyzed by several proteolytic enzymes. These morphological and chemical observations suggested that protein was a significant component of the foliar globules. Although they might also have a significant mineral content, the foliar globules were not effective as nucleators of CaCO3 crystal formation at low levels of supersaturation in artificial seawater. Overall, the results suggested that molecules of oyster shell protein may agglomerate and combine with mineral to form a surface of complex topography that coats the calcite laths but exhibits no obvious correspondence to any specific crystallographic plane.