PRP's act as highly potent inhibitors of crystal growth of calcium phosphates. They provide a protective and reparative environment for dental enamel which is important for the integrity of the teeth. Proteolytically cleaved; PRP-2, PRP-1, PIF-S and Db-S yield PRP-4, PRP-3 (protein A), PIF-F and Db-F, respectively. An hexuronic acid was shown to be linked to Ser-33 in about 40% of the polypeptides. Neither the structure of the carbohydrate (whether glucuronic acid or an isomer of), nor the linkage (whether a glycoside or an ester) has been definitely established. Sequence shown is that of allele PRH2-2, also known as PR-2; Allele PRH2-1 is also known as PR-1 or protein C, and allele PRH2-3 as PR-1'. The PRH1-DB allele (about 16% of the population) has an insertion of 21 repeated amino acids compared to the more frequent PRH1-PIF allele (68%). In contrast to all other PRH1 and PRH2 alleles, the PRH1-PA allele (16%) is not proteolytically cleaved. Extended C-terminus. Extended C-terminus.