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 struct ure, as well as to promote formation of the next mineral layer. Some i nsights into the nature of the sheets were revealed by atomic force mi croscopy (AFM) of surfaces of freshly cleaved fragments of oyster shel l folia. Visible in the micrographs were arrays of globular structures that resembled the globules seen in isolated oyster shell protein bou nd to calcite, mica, and glass. The results of chemical treatment show ed that the foliar globules slowly dissolved in 5.25% NaOCl or 1 N NaO H, reacted with an antibody prepared against an isolated oyster shell protein, and were hydrolyzed by several proteolytic enzymes. These mor phological and chemical observations suggested that protein was a sign ificant component of the foliar globules. Although they might also hav e a significant mineral content, the foliar globules were not effectiv e as nucleators of CaCO3 crystal formation at low levels of supersatur ation in artificial seawater. Overall, the results suggested that mole cules 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 crystallographi c plane.