ATP-ase activity in the odontoblastic layer of rat incisor. Determination with a radiochemical and a colorimetric...

The ATP-splitting enzyme activity in odontoblasts isolated from rat incisors has been studied by means of a radiochemical and a colorimetric micromethod. The results with the two methods were virtually identical. The reaction was linear with time for at least 45 min. The pH optimum was found to be 9.8 independently of the ATP concentration. Maximal substrate saturation occurred at a total ATP concentration of 3 mM. Ca2+ and Mg2+ ions activated ATP degradation. F-ions did not affect the activity at low concentrations, whereas higher concentrations were inhibitory. Na+ and ions were slightly inhibitory. Urea inhibited the enzyme activity at concentrations above 1.5 M, while EDTA and EGTA were strong inhibitors at very low concentrations. When incubating in the presence of low concentrations of specific inhibitors for nonspecific alkaline phosphatase, levamisole and R8231, about 20% ATP degrading enzyme activity remained. In conclusion it is suggested that there are at least two ATP degrading phosphatases active at alkaline pH.