The interaction of proteins with hydroxyapatite: I. Role of protein charge and structure

Abstract

The criteria for elution of proteins from hydroxyapatite columns were examined as a function of (1) protein isoelectric point (22 proteins with isoelectric points between 3.5 and 11.0); (2) ionic nature of eluant (Na salts of PO 4, F −, Cl −, SCN −, ClO 4 −, and CaCl 2); and (3) structural differences between related proteins. It was found that proteins can be classified into three groups: (1) basic proteins, which elute at similar, moderate molarities of PO 4, F −, Cl −, SCN −, and ClO 4 −, and low (<0.003 m) Ca 2+; (2) acidic proteins which elute at about equal moderate molarities of PO 4 and F −, but do not elute with Ca 2+ and usually not with Cl −; (3) neutral proteins, which elute with PO 4, F −, and Cl −, but show a strong anion specificity, and do not elute with Ca 2+ or SCN −. Furthermore, individual specific polar groups are not in general crucial to binding or desorption, and variations in structure, other than major loosening, do not influence strongly the pattern of protein-hydroxyapatite interaction.