We have previously shown that the mineral in granules of synthetic octacalcium phosphate (OCP) implanted subperiosteally in mouse calvariae was converted to apatitic crystals and that the OCP implantation stimulated bone formation. The matrix components accumulated on the converted apatite were very similar to those of bone nodules (starting locus of calcification) in intramembranous osteogenesis. In the present study, the nature of the matrices accumulated on OCP implants in calvariae was compared with that of the matrices accumulated in abdominal subcutaneous implants. The comparison was facilitated by the use of Maclura pomifera agglutinin (MPA) lectin which is known to have a high affinity for the primary intramembranous bone matrix. Micro-beam x-ray diffraction indicated conversion of the implanted OCP to apatitic crystals in situ, both in subperiosteal and subcutaneous sites, after 10 days. Additional bone formation was detected on the converted apatite after 13 days in subperiosteal implantation, whereas bone was not formed in the subcutaneous implantation. MPA reaction was strongly manifested after 10 days in matrices accumulated on the converted apatite in both subperiosteal and subcutaneous implantations. Biochemical data showed that intensely and weakly MPA-blotted molecules (53.0 and 152.6 kDa, respectively) were in all the mouse sera, in the guanidine HCI-EDTA extracts of mouse calvarial bone and in the extracts of the implanted OCP in both subperiosteal and subcutaneous sites. These findings indicated that the glycoconjugates accumulated on the converted apatite from OCP were similar to the glycoconjugates in the serum in terms of reactivity with MPA and molecular weights. Furthermore, the results suggest that MPA-binding glycoconjugates which had accumulated on the converted apatite may be a requisite for the differentiation of mesenchymal cells into osteoblasts in periosteum but not in subcutaneous sites.
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