The bovine dentin matrix still contains some noncollagenous proteins after thorough extraction and decalcification. These have been obtained following digestion of the matrix by cyanogen bromide. Peptides containing non-collagenous portions were isolated by chromatography on diethylaminoethyl cellulose columns and fractionated on hydroxyapatite columns. Several fractions were obtained. The principal component was a complex between a highly-phosphorylated serine-aspartic acid-rich protein and a collagen peptide. These collagenous and non-collagenous moieties could not be separated from each other even under highly dissociative solvent conditions. After digestion with collagenase, the resulting phosphoprotein fraction still contained a few residues of hydroxyproline and hydroxylysine, and an enhanced content of proline, compared to the equivalent directly extractable phosphophoryn of the matrix. These data were interpreted as indicating that the phosphophoryn which is not extractable in 0.5M ethylenediaminetetraacetic acid is in fact covalently bound to some specific section of the matrix collagen. The covalent modification of the collagen matrix with highly acidic phosphoproteins may have an important role in the mineralization process.

Time course studies of the incorporation of radioactive 2-aminoethylphosphonic acid (AEP) into the tissues of rats demonstrated that maximum incorporation into the liver lipids occurred within 12 to 30 hr after injection, compared to 2 to 3 hr for the incorporation of phosphorylethanolamine. Little incorporation of AEP was observed in the other tissues investigated (heart, lung, spleen, adipose, kidney). The AEP was incorporated to the greatest extent into 1,2-diacylglyceryl-aminoethylphosphonate (diacylglyceryl-AEP), the phosphonate analogue of phosphatidylethanolamine, with some incorporation into the lyso derivative. Diacylglycerol-AEP apparently was not further metabolized by the rat; no methylation of diacylglyceryl-AEP to phosphonolecithin was observed. Subcellular fractionation was performed on the livers of rats who received (3)H-AEP 12,30,36, and 48 hr prior to sacrifice. The greatest amount of radioactivity was recovered in the soluble fractions. Lipid extraction was performed on the subcellular fractions, and most of the radioactivity present in the lipids was found in the microsomal fraction, with the next highest recovery in the mitochondrial and nuclear fractions