Studies On The Mechanism Of The Nacre Formation Of Pearl Oyster Pinctada Fucata

From the outer side to the inner side, the shell of Pinctada fucata is composed of periostracum, the prismatic layer and the nacreous layer. The nacre is identical to pearl in nature. Therefore, the study on the mechanism of nacre formation would facilitate the understanding of the way of pearl formation and promote the development of related subjects. In this study, we have explored the mechanism of nacre formation from angles of the structure of shell (the inner shell film), the matrix protein from nacre and the related protein of nacre formation from mantle (the calmodulin-like protein).We found that the film is not homogeneous in different area of the shell. The inner shell film in the extrapallial zone consists of two films under certain state. The proteins of the inner shell film are simple and they are composed of framework proteins of the shell. The calcium carbonate crystallization experiments indicated that the proteins of the inner shell film can inhibit the growth of calcite and accelerate the precipitation of calcium carbonate crystals. Maybe in this way the inner shell film facilitate the nacre formation.The inner shell film was detached form the nacre and we developed a new biomineralization system with the film in vitro. The function of soluble proteins from the nacre was changed in the new system (from inhibiting the growth of calcite to inducing the precipitation of flatted aragonite). We think the soluble nacre protein (combined with the inner shell film) can not only induce the growth of aragonite, but regulate the growth direction of aragonite, and maybe in this way to regulate the growth of nacre.A novel non-acidic matrix protein (N40) was purified from the nacre. N40 was considered as a silk-like protein in shell because it is rich in Gly and Ala. The crystallization experiment showed that N40 can facilitate the growth of aragonite and it was thought to promote the precipitation of nacre in this way. The function of N40 is important complementarities to the popular model of the structure of the organic matrix of nacre. We have detected a putative CaLP binding protein in the nacre proteins with the recombinant CaLP. It is suggested that CaLP can induce the growth of aragonite through combined with the binding protein. The immunochemical study showed that CaLP may locate around the prisms and in the organic layer sandwiched between the prismatic layer and the nacre. We deduced that CaLP may be multifunctional in the course of shell formation: it can not only regulate the prisms growth, but participate in the initiation of nacre growth in the organic layer (in a state of binding to the basic framework proteins) through combining to the binding protein of the nacre.