AMINO ACIDS AT NUCLEATING SITE IN MINERALIZING ELASTIC TISSUE

Previous studies have implicated ferric ion bound to matrix sulfhydryl as the nucleating species inducing the deposition of hydroxyapatite in elastic tissue in vitro. In this study it was assumed that formation of a mineral phase would block the access of proteolytic enzymes to those regions of the matrix involved in nucleation and binding of mineral, while nonessential portions of the matrix would be removed. Mineral was found to be concentrated in the residue after proteolysis. The cysteine content as determined by cysteic acid of the residue left after elastase treatment of calcified elastin" was five times that of the residue from uncalcified elastin. The cysteine content of the residue protected by mineral was highest during the nucleation phase. Fe3+ was also found to be concentrated in the calcified residue after digestion. The data indicated that one mole of iron was bound per mole of cysteine sulfhydryl. It is postulated that iron bound to matrix cysteine is at the nucleation site in elastic tissue. © 1969 Springer-Verlag."