Adsorption and modification of calcium salt crystal growth by anionic peptides and spermine.

Synthetic polyanions, including peptide analogs of naturally occurring proteins, have been shown to inhibit the nucleation and growth of calcium salt crystals. The binding characteristics of polyaspartate and aspartate-serine copolymers to calcium carbonate (calcite) and hydroxyapatite (HAP) are presented here. The binding is related to dose-dependent inhibition of crystal growth measured by constant composition assay. Peptide phosphorylation had little effect on binding affinity or crystal growth inhibition with either calcium salt. Spermine was able to reduce hydroxyapatite crystal growth but with lower efficacy than the polyanionic peptides. Spermine reversed some of the HAP growth inhibition produced by an anionic peptide. Binding of a labeled polyanion was reduced by a similar anionic peptide at all concentrations of the label, however, spermine reduced binding only at higher concentrations of the labeled polyanion. The data support the presence of multiple binding site classes on HAP surfaces, some inaccessible to polycations and some at which both polyanions and polycations can bind.