Separation by polyacrylamide gel electrophoresis of multiple proteases in rat and bovine enamel

At least seven protein bands of protease activity were found in rat secretory enamel and six bands in bovine secretory enamel. The bovine proteases had molecular weights similar to those found in rat enamel. Two bands were found to be active in gels containing enamel proteins. All proteases were acid-resistant and calcium-dependent. In vitro digestion of secretory enamel resulted in a changing profile of proteases. Rat maturation enamel contained a 23,000 and a 33,000 molecular-weight protease which were not present in the secretory enamel. The 33,000 molecular weight protease was also active against enamel proteins. Thus multiple proteases are present in rat and bovine secretory enamel and in rat maturation enamel; some of these may be important in hydrolysis of enamel proteins.