Protein profile of pepsin-digested carious and sound human dentine

The purpose of this study was to describe the protein profile of pepsin-digested carious and sound dentine using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Carious and sound dentine powder was decalcified using 10% EDTA at pH 7.4 for 48 h. The decalcified pellet was digested using pepsin at pH 2 under sequenced conditions: at 4 degrees C for 24 h, a further 24 h at 23 degrees C, and finally for 24 h at 37 degrees C. After every step, the soluble fraction was separated by centrifugation and analyzed in 15% SDS-PAGE. Two bands at 56 and 62 kDa could be observed in carious dentine digests and were considered specific carious bands. Similar bands could be observed in sound dentine samples, but only after pepsin digestion at higher temperatures (23 degrees C and 37 degrees C). Pepsin digests non-helical collagen and the triple helix structure of collagen is lost when the temperature rises. The bands at 56 and 62 kDa in sound dentine specimens thus represent pepsin-cleaved collagen. There is a possibility that the specific carious bands in carious dentine represent collagen decomposed in a manner similar to the way pepsin digests native dentine collagen at 23 degrees C and 37 degrees C.