Fractionation of the acid-soluble nitrogen of bone and dentine

Abstract

The proportion of the total nitrogen of ox bone and human dentine soluble in N HCl at 2 °C was estimated and the material fractionated by gel filtration and ion-exchange chromatography. Sawn discs of bone were split into fragments in a percussion mill, while root dentine was prepared with the minimum of grinding necessary to remove cementum and pulp. Bone fragments and dentine “roots” were demineralized without further mechanical treatment. Under these conditions 3.7 per cent of bone nitrogen and 4.3 per cent of that of dentine went into solution. The large-molecular fractions contained very little soluble collagen and included only a small proportion of the non-collagenous components known to be present in bone, while the corresponding fractions from dentine comprised only one quarter of the total acid soluble nitrogen. The small-molecular fractions, consisting of peptides and only minimal traces of free amino acids, comprised 11 per cent of the soluble nitrogen of bone and 27 per cent of that of dentine. Acid demineralization, under the standard conditions described, was found to be perfectly adequate and very convenient for the isolation of these peptide fractions but unsuitable for the isolation of the compounds of larger molecular size.