ウシ歯胚の象牙芽細胞層およびエナメル芽細胞層における乳酸脱水素酵素含有基質小胞様小胞に関する研究

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Matrix vesicles, membrane invested vesicles, are generally accepted to initiate mineralization in the extracellular matrix of calcifying tissues except enamel. Matrix vesicles contain high alkaline phosphatase activity and related phosphatase activities associated with the plasma membrane ; this may be because matrix vesicles may be formed by budding from the plasma membrane of calcifying cells. Recently, lactate dehydrogenase (LDH)-containing vesicles were found in the epiphyseal growth cartilage [Hosokawa et al. (1988) J. Biol. Chem. 263, 10045-10047] and the resting cartilage [Ohashi-Takeuchi et al. (1990) Biochem. J. 266, 309-312], and in the calvaria of mice [Naito (1992) J. Kyushu Dent. Soc. 46, 345-354]. However, it is unknown what true function of LDH-containing vesicles is and there is no report on the presence of LDH-containing vesicles in calcification sites of developmental tooth germs. In the present study, LDH-containing vesicles were found to be present in odontoblast layer and ameloblast layer of bovine tooth germs, as follows. 1. The extracellular matrix vesicle fraction was prepared from odontoblast layer of bovine tooth germs. Only in the presence of detergents, LDH activity was detected in the extracellular matrix vesicle fraction, showing that LDH is located in the vesicles. 2. The extracellular matrix vesicle fraction of bovine odontoblast layer was subjected to sucrose density gradient centrifugation. LDH activity was detected in the presence of Triton X-100 but not in the absence of Triton X-100. The sedimentation profiles of LDH in the presence of Triton X-100 were different from that of alkaline phosphatase, showing that LDH-containing vesicles were different from matrix vesicles. 3. Odontoblast fraction from bovine tooth germs was homogenized with isotonic solution and then subjected to sucrose density gradient centrifugation. LDH activity was recovered only in the soluble top fraction, but not in sediment, showing that LDH in the vesicles is not simply encapsulated by vesicles from the plasma membranes or membranes of intracellular organelles. 4. Electrophoretic profiles of LDH isoenzymes from the extracellular matrix vesicle fraction of bovine odontoblast layer were similar to those of cytosolic LDH of bovine odontoblast, suggesting that the presence of a mechanism for the specific uptake of cytosolic lactate dehydrogenase into vesicles. 5. Furthermore, LDH-containing vesicles were found in the ameloblast layer of bovine enamel organ. The existence of LDH-containing vesicles in bovine ameloblast layer, where calcification is not initiated by matrix vesicles, suggests the possibility that LDH-containing vesicles have a specific role different from matrix vesicles.
九州歯科学会の論文
1992-12-25

ウシ歯胚の象牙芽細胞層およびエナメル芽細胞層における乳酸脱水素酵素含有基質小胞様小胞に関する研究

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