Systematic purification of free and matrix-bound phosphophoryns of bovine dentin: Presence of matrix-bound phosphophoryn as a distinct molecular entity

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Abstract
Free and matrix-bound phosphophoryns, both highly phosphorylated proteins in dentin, were prepared from EDTA extract and CNBr-digests of bovine dentin. The two components were purified by DEAE-cellulose, SP-Sephadex, and gel filtration chromatography. The matrix-bound component was eluted as a distinct peak from the free component in the above chromatographic systems. Amino acid composition of the purified matrixbound component indicated that this component consisted of phosphophoryn and collagen in the ratio of 2:3 based on the number of the residues. The matrix-bound component could not be reconstituted by mixing phosphophoryn with collagen CNBr peptides. Artificial crosslink products of free phosphophoryn and collagen CNBr-peptides by the carbodiimide method showed similar properties to the physiological matrix-bound phosphophoryn. The bond between phosphophoryn and collagen of the matrix-bound component is assumed to be a covalent crosslink.