Comparison of inhibitory activity on calcium phosphate precipitation by acidic proline-rich proteins, statherin, and histatin-1

This study quantitatively compares the inhibition of calcium phosphate (CaP) precipitation by the salivary acidic proline-rich proteins (PRPs) statherin and histatin-1. Saliva and CaCl₂ in 125 mM imidazole buffer (pH 7.0) were incubated with potassium phosphate and a hydroxyapatite (HAP) suspension, for 30 min at 25°C, then filtered through nitrocellulose. The calcium (Ca) concentration in the filtrate was measured by atomic absorption spectrophotometry, then deducted from that in the initial solution to determine the amount of CaP precipitation after 30 min. The values of the inhibitory activities on CaP precipitation relative to crude parotid saliva were 4.7, 4.9, 6.9, and 65.8 for histatin-1, large PRPs, small PRPs, and statherin, respectively.