Effect of the Cysteine-Rich Mdm2 Peptide in the Crystal Growth of Hydroxyapatite in Aqueous Solution

The crystal growth of hydroxyapatite (HAP), the most stable calcium phosphate phase at 37 °C, pH 7.40, and ionic strength of 0.15 M NaCl, in the presence of the cysteine-rich Mdm2 peptide (containing 48 aminoacids in ring finger configuration) has been investigated by the constant composition technique. Crystallization took place exclusively on well-characterized HAP crystals in supersaturated solutions only with respect to this calcium phosphate salt. The kinetic results indicated a surface diffusion spiral growth mechanism. The presence of the Mdm2 peptide inhibited the crystal growth of HAP by 59−92% through adsorption onto the active growth sites of the HAP crystal surface. The kinetic results favored a Langmuir-type adsorption model, and the value of the calculated affinity constant was kaff = (258 ± 21) × 104 dm3 mol-1.