In vivo cleavage of dentin phosphophoryn following beta elimination of its phosphoserine residues.

Phosphophoryn, a unique phosphoprotein in dentin, has a polydisperse character. Keto acid was found to be present in this protein by condensation reaction with dinitrophenyl (DNP)-hydrazine and was identified to be pyruvate from the result that [3H]lactate was formed by the reduction of phosphophoryn with [3H]NaBH4. In the case of phosvitin, incorporation of DNP-hydrazine was much less than in phosphophoryn, even after the same treatment as the extraction procedure of phosphophoryn. DNP-hydrazine incorporation was much higher in the phosphophoryn of mature dentin than in dentin of unerupted teeth. From these results, pyruvate was though to be formed time dependently in vivo by beta elimination of phosphoserine residues and subsequent cleavage of the peptide chain, which may contribute to the polydispersity of phosphophoryn.