Demonstration of a K+-stimulated and ouabain-sensitive p-nitrophenyl phosphatase activity in enamel-and dentin-forming tissues in the rat.

p-Nitrophenyl phosphate hydrolysis was studied at neutral pH with tissue preparations of the rat secretory and maturation enamel organs and dental pulp. By introduction of inhibitors to nonspecific alkaline phosphatase activity and stimulants to the K+-stimulated and ouabain-sensitive p-nitrophenyl phosphatase activity, the latter enzyme activity could be demonstrated. This enzyme activity is generally held to be representative of the enzyme sodium- and potassium-stimulated adenosine triphosphatase. The K+-stimulated activity was magnesium dependent and highly sensitive to fluoride. It was inhibited completely by 3 mM fluoride in the incubation medium and about 1 mM produced half the maximum inhibition. The K+-independent enzyme activity was inhibited 50-60% by fluoride in concentrations between 3 and 15 mM. The high fluoride sensitivity of the K+-stimulated activity may perhaps help to explain the vulnerability of dental tissues to fluoride.