Immunolocalization of an acid phosphatase from pearl oyster (Pinctada fucata) and its in vitro effects on calcium carbonate crystal formation.

Distribution of an acid phosphatase, AcPase I, from pearl oyster (Pinctada fucata) in different tissues was investigated via enzyme activity determination and immunohistochemistry. Positive reactions were observed in sections of digestive gland, base of gill filaments, and epithelia of the outer side of the middle fold and the inner side of the outer fold, which indicated AcPase I might participate in processes besides immune defense, such as calcium metabolism or shell formation. Its effects on CaCO(3) crystal formation were studied in vitro. Results revealed that AcPase I inhibited CaCO(3) precipitation in a dose-dependent manner and had no affinity for calcium. CaCO(3) crystals induced by AcPase I exhibited a cluster needle-like morphology, which proved to be aragonite. The morphology and size of the aragonites varied with different concentrations of AcPase I. Our observations described here may provide important clues to further understanding of the correlations between mineralization and immune defense in the oyster.