The hydrolysis rates of ATP and phosphoserine in the odontoblast-predentin region of intact and carious human teeth.

Coronal odontoblast-predentin tissue was taken from intact teeth and from teeth with carious lesions of varying depths, and the samples (20, 200 x g, saline-soluble fractions) were studied for their ability to hydrolyze adenosine triphosphate (ATP) and phosphoserine. A significantly higher rate of ATP hydrolysis at pH 9.8 was detected in enamel caries and a significantly lower rate in advanced caries than in intact teeth. The rates of the hydrolysis of phosphoserine at pH 9.8 did not differ between the various tooth groups, and the only clear trend indicating elevated enzyme activity was seen in the group of initial dentin caries. The ATP and phosphoserine hydrolysis at pH 9.8 were considered to have been due to the nonspecific alkaline phosphatase (EC 3.1.3.1) activity. In the presence of both levamisole and ouabain, maximal enzyme-dependent ATP hydrolysis was observed at pH 7.9. The remaining ATP-cleaving activity was thought to have been due to the Ca2+Mg2+-dependent ATPase (EC 3.6.1.3). The Ca2+Mg2+-dependent ATPase activities at pH 7.9 remained at constant levels in both the intact and carious groups. The parameters studied in vitro were thought to reflect changes in the mineralization rate of reparative dentin as a response to caries in vivo.