Unraveling the role of E. coli and calf intestinal alkaline phosphatase in calcium phosphate synthesis

The enzyme-catalyzed synthesis of calcium phosphate is a promising method for producing calcium-based nanomaterials for biomedical applications. The purpose of this work was to determine the type of phosphate that forms when alkaline phosphatase catalyzes the reaction, and to identify the role of natural biopolymers in calcium phosphate formation. In this research, we analyzed calcium phosphates that were synthesized in the presence of alkaline phosphatase from either E. coli or calf intestinal, analyzed the obtained nanoparticles and compared them by functional composition, elemental ratio, and morphology. Since all syntheses were performed in Tris buffer with the addition of MgCl₂, the final depleted hydroxyapatite incorporated magnesium. It was found that in the first 24 h, the reaction product form is determined by the enzyme source as well as the presence of other biopolymers (in particular, humic acid) in the reaction mixture. Hollow nanospheres of the depleted hydroxyapatite were obtained as a final product for both E. coli and calf-intestinal alkaline phosphatase during a 7-day reaction. When humic acid was added into the reaction mixture, separate spheres of the depleted hydroxyapatite were observed during a 24-h reaction. When Mg ions are present in the reaction mixture as a buffer component, they are evenly incorporated into the structure of the resulting calcium phosphate. The data obtained can be useful in understanding the calcification process of bioobjects and in applying the enzymatic method of calcium phosphate synthesis to biomedical applications.