Proteins in the enamel fluid of immature porcine teeth.

The fluid was separated from the immature soft enamel of porcine permanent teeth in the secretory stage according to procedures reported previously (Aoba and Moreno, 1987). The protein content of the fluid was about 2.8% w/v; its amino-acid composition was characterized by high contents of Pro, Glx, Leu, and His, showing composition similar to that of the 20 kilo-dalton (kd) amelogenin or its C-terminal segments. The two major protein species in the fluid had apparent molecular weights of 13 kd and 11 kd, as determined by SDS electrophoresis; the N-terminal residue of the former was Leu, while that of the latter was Ala. The C-terminal sequence of both of them was -Met-Phe-Ser. By comparison with the published sequence of 20-kd porcine amelogenin, it is concluded that the main fluid constituents were derived by cleavages of N-terminal segments from the 20-kd amelogenin.