Layered calcium phenyl phosphate ((C(6)H(5)PO(4))(0.92)(HPO(4))(0.08)Ca center dot 1.3H(2)O: CaPP), which is composed of a multilayer alternating bimolecular layer of phenyl groups and amorphous calcium phosphate phase, was treated in aqueous media including different amounts of enzyme such as alkaline phosphatase (ALP) at pH = 9.6 and 37 degrees C for 48 h. Treating the CaPP in the absence of ALP took place only the dissolution of this material. When the CaPP particles were treated in the presence ALP, calcium hydroxyapatite (Ca(10)(PO(4))(6)(OH)(2): Hap) was formed. The yielded Hap contained no phenyl group and the molar ratio Ca/P of this material was 1.66, almost corresponding to 1.67 of the stoichiometric Ca/P ratio of Hap. TEM observation revealed that the irregular-shaped CaPP particles disappeared and rod-shaped Hap nanoparticles were generated. The particle length and crystallite size of Hap were slightly increased on increasing the additive amount of ALP. These facts allow us to infer that the CaPP particles are dissolved, hydrolyzed and recrystallized to Hap by treating with ALP in aqueous media at body temperature of 37 degrees C and that the ALP plays as a catalyst for hydrolysis of phenyl phosphate ions. This phase transformation of CaPP in Hap in the presence of ALP resembles to the formation mechanism of Hap in animal organism. (C) 2009 Elsevier Ltd. All rights reserved.