Adsorption of naturally occurring polymers onto calcium oxalate crystal surfaces

The adsorption of proteins and mucopolysaccharides on calcium oxalate crystals was measured by solution depletion. Anionic protein adsorption was found to be sensitive to calcium ion concentration. Adsorption of fibrinogen was anomalously large in the presence of 0.01 M Ca2+. Adsorption of cationic protein (histone) was sensitive to oxalate ion concentration. A small alteration in adsorption of protein as a result of pH or temperature change was also observed. Plots of adsorption versus concentration were interpreted in terms of a Langmuir adsorption isotherm. The derived Langmuir adsorption parameters were then used to investigate the contribution of protein, by physical adsorpti, to the quantity of matrix in urinary stones. It was concluded that physical adsorption can account for the deposition of part but not all of the matrix in calcium oxalate stones. It was also concluded that physical adsorption of mucopolysaccharides by calcium oxalate crystals could explain the inhibition of growth and aggregation of calcium oxalate crystals seen with in vitro precipitation systems. Recalculation of published data indicates that adsorption of protein on dental enamel (calcium hydroxyapatite) results in approximately the same extent of surface coverage as adsorption on calcium oxalate crystals, but protein has a much lower affinity for dental enamel than for calcium oxalate crystals.