A comparative study of the adsorption of amino acids on to calcium minerals found in renal calculi

Abstract

To assess the binding of individual amino acids to the principal calcium minerals found in human kidney stones, the adsorption of 20 amino acids on to calcium oxalate monohydrate, CaHPO4*2H2O, Ca3(PO4)2 and Ca5(PO4)3OH crystals was determined over the physiological urinary pH range (pH 5-8) in aqueous solutions. All amino acids adsorbed most strongly at pH 5, and this decreased in all cases as the pH was increased. The amino acids which adsorbed most strongly were aspartic acid, glutamic acid and gamma-carboxyglutamic acid, with the last displaying the strongest affinity. All amino acids bound more avidly to calcium oxalate monohydrate than to any of the phosphate minerals. Adsorption on to CaHPO4*2H2O was generally higher than for Ca3(PO4)2 and Ca5(PO4)3OH, for which all amino acids, with the exception of gamma-carboxyglutamic acid, had only a weak affinity. The binding affinity of these acids is thought to be due to their zwitterions being able to adopt conformations in which two carboxyl groups, and possibly the amino group, can interact with the mineral surface without further rotation. The strong binding affinity of di-and tri-carboxylic acids for calcium stone minerals indicates that proteins rich in these amino acids are more likely to play a functional role in stone pathogenesis than those possessing only a few such residues. These findings, as well as the preferential adsorption of the amino acids for calcium oxalate monohydrate rather than calcium phosphate minerals, have ramifications for research aimed at discovering the true role of proteins in stone formation and for potential application in the design of synthetic peptides for use in stone therapy.

Adsorption and bioactivity studies of albumin onto hydroxyapatite surface

“…The BSA layer acted as I shield against HA surface dissolution, reducing the precipitation of the new bioactive calcium phosphate phase. The affinity of BSA with calcium ions by the charged amino acids residues of the protein might also contribute to the difference on calcium precipitation in favor of HA + BSA discs [25,26].…”

The influence of amino acids on the formation of nanocrystalline hydroxyapatite

“…Most likely, this is associated with the fact that, under the experimental conditions, the amino acids in the form of ions [ + NH 3 CH 2 COO -, − OOCCH(NH 3 ) + CH 2 COO -, − OOCCH(NH 3 ) + (CH 2 ) 2 COO -, + H 3 N(CH 2 ) 4 CH( + NH 3 )COO -], which are capable of sorbing on both positively and negatively charged regions of the hydroxyapatite particles, predominantly exist in the aqueous solutions. The presence of zwitterions in the solution favors the stabilization of conformers for which the interaction of amino and carboxyl groups with the particle surface occurs without changing the molecular conformation, i.e., is energetically more favorable [2]. An additional stabilization of the newly formed surface compounds can be governed by the ability of the amino acids to form polydentate chelate complexes with calcium ions.…”

“…In particular, Fleming et al [2] experimentally investigated the adsorption of amine acids on crystals of the stoichiometric apatite (Ca/P = 1.67) [2]. The effect of amino acids on the kinetics of apatite crystallization was experimentally studied by Koutsopoulos and Dalas [3].…”

“…Considerable progress in the investigation of the regularities of the phase formation in biological media can be achieved using model experiments [2,3]. In this respect, the present paper is devoted to the investigation into the influence of amino acids on the formation of synthetic analogs of hydroxyapatites of renal calculi (uroliths).…”

“…It is known that amino acids contained in a urine substantially affect the formation of phases of pathogenic aggregates [2,4,5]. In particular, Fleming et al [2] experimentally investigated the adsorption of amine acids on crystals of the stoichiometric apatite (Ca/P = 1.67) [2].…”