Enzyme Activity at Hydroxyapatite Surfaces

The effect of hydroxyapatite on the activity of alkaline and acid phosphatase was studied in a simple in vitro system. Alkaline phosphatase had a reduced activity in the absorbed state, and the pH-optimum for the adsorbed enzyme had decreased with one-half pH unit. The acid phosphatase was not influenced by the apatite in the presence of substrate. When no substrate stabilized the enzyme, a reduction was observed. This reduction was larger at pH values close to the pH-optimum for the enzyme.