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Abstract:
The role of matrix vesicles in the calcification process was investigated in vitro. Isolated vesicles were unable to transport calcium actively. The ATPase activity was not stimulated by calcium in the presence of an optimal magnesium concentration. At a physiological substrate concentration of pyrophosphate, the pyrophosphatase had a pH optimum around 7.0. The vesicles nucleated calcium phosphate precipitation independently of the presence of hydrolyzable phosphate compounds. It is suggested that vesicles induce calcification by nucleating calcium phosphate precipitation and through the local destruction of pyrophosphate, a crystallization inhibitor.