Microheterogeneous Collagen Model on the Basis of a Chromatographic Study on Hydroxyapatite Columns

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Abstract
Earlier, on the basis of experimental chromatograms of collagen obtained on hydroxyapatite columns, a microheterogeneous collagen model with fluctuating primary structures around a mean structure was proposed. In this paper this model is examined in detail on the basis of a new chromatographic theory. Good fits were obtained between theory and experiment. It was estimated that the probability, π, that aspartic and glutamic residues exist at correct positions on the three α collagen peptide chains is about 0.8. The following conclusions were derived at the same time: (a) the energy of adsorption, ∊, for a carboxyl group of collagen on to a crystal site of hydroxyapatite is 0.7 kcal/mol. (b) The replusive interaction energy, [Etilde], for one of collagen molecules with another on the crystal surface is 3 kcal/mol when these make maximum contact. (c) The square-root, h', of the area on the collegen surface where a carboxyl group can move freely (around the mean position) is 2.5-3.5 Å. (d) It is likely that a considerable adsorption of phosphate ions from the buffer occurs on the collagen surface adsorbed on the hydroxyapatite surface. The experimental values obtained in (a)–(c) are all reasonable ones; this strongly supports the microheterogeneous model itself. It is suggested that the ambiguous primary structure arises at a translational level of biosynthesis.