Biochemical characterization of alkaline phosphatase from partly mineralized bovine enamel

Alkaline phosphatase (AP) from partly mineralized bovine enamel was studied. The enzyme resembles alkaline phosphatases in other calcifying tissues. The Km was 0.46 mM; the phosphatase was strongly inhibited by 1 mM Levamisol or EDTA and it showed the same sensitivity towards heating as bone alkaline phosphatase. The inactivation caused by phosphate ions was approximately about 30%. In a zymogram, five isozymes of enamel alkaline phosphatase can be recognized. In a SDS-polyacrylamide gel a single band showing enzyme activity was visualized. This enzyme has an apparent molecular weight of 140,000.