Alkaline phosphatase in the enamel organ of the rat incisor.

Abstract

abstract— The distribution of alkaline phosphatase in the enamel organ of the rat incisor was histochemically investigated using α‐naphthyl phosphate as the substrate. During the stage of enamel matrix formation the enzyme activity was found mainly in the stratum intermedium, while during the stage of enamel maturation the activity was evenly distributed within the enamel organ. The biochemical properties of alkaline phosphatase, using paranitrophenyl phosphate as the substrate, were studied. The pH optimum of the enzyme was found to be about 10. The heat inactivation of alkaline phosphatase from the enamel organ was found to be similar to the behavior of bone and odontoblast phosphatase. Mg2+ activated the enzyme, while Ca2+, PO43− and F− inhibited the enzyme. The effect of urea on the enzyme activity was similar to the behavior of bone and odontoblast phosphatase. EDTA treatment resulted in a marked inhibition of the activity of alkaline phosphatase. It was concluded that there was no detectable difference in biochemical behavior between alkaline phosphatase in the stage of matrix formation and the stage of enamel maturation. It was also concluded that alkaline phosphatase from the enamel organ is similar to the alkaline phosphatase from bone and odontoblasts.