Dipeptidyl-peptidase II and cathepsin B activities in amelogenesis of the rat incisor

A body of published evidence suggests that a significant portion of enamel matrix protein synthesized by ameloblasts localises in the lysosomal-endoso mal organelles of these enamel organ cells. Little is known regarding the l ysosomal proteolytic activities during amelogenesis. The aims of this study were to detect and measure the activities of lysosomal peptidases cathepsi n B (E.C. 3.4.22.1) and dipeptidyl-peptidase II (E.C. 3.4.14.2) in the enam el organ of the rat incisor and to ascertain whether rat enamel matrix prot eins are degraded by these peptidases in vitro. Whole enamel organs were di ssected from rat mandibular incisors. Enamel protein was also collected fro m the rat teeth. Analysis indicated that the rat incisor enamel organs cont ained specific activities of both dipeptidyl-peptidase II and cathepsin B a t levels comparable with those of kidney which is rich in both these lysoso mal peptidases. Gel electrophoresis and immunoblotting demonstrated that bo th cathepsin B and dipeptidyl-peptidase II were able to substantially degra de the rat enamel proteins in vitro. Based on these observations, we propos e that lysosomal proteases have roles in amelogenesis in the intracellular degradation of amelogenins.