QUANTITATIVE-ANALYSIS OF AMELOGENIN SOLUBILITY

Amelogenins are a group of extracellular enamel matrix proteins which are believed to be involved in the regulation of the size and habits o f forming enamel crystals. The aim of this study was to compare the so lubility properties of several amelogenins at various pH (from 4.0 to 9.0) at constant ionic strength (IS), and to examine the influence of buffer composition, IS, and divalent metal ions (including Ca2+, Mg2+, and Zn2+) on amelogenin solubility. The solubility of the recombinant murine amelogenin (''rM179'') was minimum near its isoelectric point and increased rapidly below and above, regardless of: buffer compositi on. A similar trend was observed for the native porcine (''25K'') amel ogenin. Porcine ''23K'' amelogenin was only sparingly soluble from pH of 4.0 to 9.0, in contrast to the analogous recombinant ''rM166'', whi ch was more soluble in acidic solutions. The synthetic amelogenin poly peptide ''TRAP'' was extremely insoluble, while synthetic LRAP was rea dily soluble. Porcine ''20K'' amelogenin solubility increased striking ly as the solution pH was lowered from 7.0 to 6.0. Increasing IS decre ased the solubility of rM179. While Zn2+ reduced rM179 solubility, Ca2 + and Mg2+ showed no significant effects. We conclude that the solubil ity of amelogenin was dependent on the primary structure, solution pH, and IS, and the low solubility of amelogenins under physiological con ditions may result from their tendency to form quaternary (aggregate) structures in vivo.