The organic matrices of the shell of the American oyster Crassostrea virginica Gmelin

The calcified shell layer of the American oyster Crassostrea virginica Gmelin consists of the calcitic prismatic layer and calcitostracum. The EDTA-insoluble matrix of the prismatic layer has a relatively high non-polar amino acid content, a common feature of calcitic prismatic layers of many bivalve species. The proteins of the prismatic layer wall matrix are shown by immunocytochemistry to be different from those of the intercrystalline matrix of the same layer. Immunocytochemical studies of both layers indicate that the insoluble matrix fraction constitutes the major framework of the matrix. The soluble matrix, with its glycosaminoglycans (GAGs), seems to be at the surface of the insoluble matrix and surrounds calcite crystals. Soluble and insoluble matrices appear to be synthesized separately, but packaged into the mucous droplets of the outer shell-side epithelium of the mantle, where they aggregate in groups and are secreted into the extrapallial cavities.