INTERACTION OF HUMAN GALLBLADDER MUCIN WITH CALCIUM HYDROXYAPATITE - BINDING-STUDIES AND THE EFFECT ON HYDROXYAPATITE FORMATION

Calcium hydroxyapatite (HAP) crystals formed in vitro in the presence of polymeric human gallbladder mucin (1.0 mg/mL) were smaller (0.75 +/ - 0.39 mu m) than control crystals (7.86 +/- 2.76 mu m), but the mucin did not affect the kinetics of crystal formation or alter the amount of mineral phase present at equilibrium. In contrast, glycopeptide sub units produced by proteolysis of the native mucin had no effect on HAP crystal size. Both native mucin and glycopeptides bound to mature HAP crystals, but the glycopeptides were much more readily displaced by p hosphate ions. Therefore, in experiments where HAP was being formed, t he phosphate ions inhibited the interaction of glycopeptides with the nascent HAP. These results indicate that gallbladder mucin may modulat e HAP formation in vivo and that this ability may be altered during pa thological states, such as neutrophil infiltration or bacterial coloni zation, that may cause the release of proteinases capable of digesting mucin.