Properties of alkaline phosphatases from cellular cementum of rat molars

The characteristics of nonspecific alkaline phosphatase, (APase, EC 3.1.3.1.) measured as beta-glycerophosphatase (GPase, EC 3.1.3.1.), inorganic pyrophosphatase (PPiase, EC 3.6.1.1.) and adenosine triphosphatase (ATPase, EC 3.6.1.3.) were studied in detail of butanol extracts prepared from rat molar cementum. Mg2+ was not absolutely essential to any of the activities, but at low levels was stimulatory in all cases. Higher concentrations were inhibitory. Ca2+ stimulated ATPase activity weakly at low levels, but was slightly inhibitory to the other enzyme activities. All enzyme activities showed nearly identical sensitivities to heat inactivation and to L-p-bromotetramisole and levamisole, which caused nearly complete inhibition. About 10-15% of the ATPase activity was insensitive to L-p-bromotetramisole and levamisole. The data are consistent with the concept that GPase, PPiase and ATPase activities of cementum to a major part stem from one enzyme, namely nonspecific alkaline phosphatase.