The ion-binding characteristics of reconstituted collagen

Abstract

The ion-binding capacity of highly purified reconstituted calf-skin collagen, and the effects of these ions on the precipitation and solubility of the collagen, were studied with a variety of salt solutions at ionic strength 0.16 and pH7.4. Only a small percentage of the total theoretically available anionic and cationic groups was available for ion-binding. In view of this, it appears that most of the ionizable groups of collagen are involved in intramolecular or intermolecular linkages, or both. Nevertheless, marked differences in the binding of the various ions by collagen were observed. Bivalent cations were bound in extremely small but remarkably similar quantities. In contrast, sodium was bound both in much higher and more variable quantities. Of the anions, pyrophosphate and sulphate were bound in the largest quantities, followed by phosphate, fluoride and chloride, in that order. Despite the minimal uptake by collagen of bivalent cations, they prevented the aggregation of tropocollagen into fibrils, and disaggregated fibrillar collagen. In the presence of multivalent anions, tropocollagen aggregated readily and its fibrillar stability was maintained. On the basis of the imbalance in the binding of ion pairs by the sodium pyrophosphate- and sodium phosphate-treated collagens, it was apparent that a reduced number of side-chain carboxyl groups were dissociated in the presence of these salts.

Formation of calcium phosphate/collagen composites through mineralization of collagen matrix

“…35 It was demonstrated that solution pH can affect the electrochemical property of collagen, such as the dissociation of the acidic and basic groups of collagen molecules 37,38 and ion-binding characteristics of collagen fibrils. 39 The isoelectric point of tropocollagen of calf skin 37 is reported to be pH 8.3 and that of pig skin gelatin 38 is approximately pH 9.4. Therefore, the more basic the solution is, the more anionic residues are available in the collagen molecules to react with Ca 2+ ions.…”

Solvent specific persistence length of molecular type I collagen

“…A second potential explanation incorporating electrostatic effects must be included: the results could also be explained by selective ion adsorption along the molecular backbone, resulting in an increased charge density that overwhelms the screening effects. The effect of selective ion adsorption was observed by Docking and Heymann and further investigated by Weinstock et al In the Weinstock study, type I collagen was suspended in solutions varying in species and concentrations of ions. The ions were then dialyzed out of solution.…”

Collagen intrafibrillar mineralization as a result of the balance between osmotic equilibrium and electroneutrality

“…Likewise, PAH-ACP should not have been attracted to the other band sites (e.g. b, c and d bands) because charges of the ionic residues in the fibrillar polyampholyte are internally compensated along those locations 24,25 .…”