Characterization of alkaline phosphatase from buccal mucosa in young rats.

Alkaline phosphatase (APase) is a plasma membrane-integrated protein with unknown function and is found in many different tissues of the body. It is normally not present in squamous epithelium. Nevertheless, it has been demonstrated in developing rat oral epithelium, where it exists together with several different phosphatases. In this study APase was solubilized from rat buccal mucosa and partially purified by gel chromatography followed by ion-exchange chromatography. Three isoenzymes with similar kinetic characteristics but different sensitivities to heat inactivation were obtained. All three had a pH optimum of 10.2 and a Michaelis-Menten constant of 0.3 mM. Combined chromatographic/electrophoretic and histochemical tissue section analysis of APase isoenzymes indicated that the buccal mucosa of young rats contains three APase isoenzymes, two of which are of epithelial origin and the third of endothelial origin.