An essential role for the 2-sulfamino group in the interaction of calcium ion with heparin

Abstract Differences in the circular dichroism and n.m.r. spectra of the sodium and calcium salts of heparin concur in suggesting that a chelate complex is formed between 1 mol of calcium ion and a disaccharide repeating segment of the polymer. Upon selective hydrolysis of the N -sulfate group of heparin, this specific binding of calcium is no longer observable. It is proposed, among other possibilities, that the carboxylic group strongly binds the cation, and that the sulfamino group of an adjacent sugar residue simultaneously engages in a weaker electrostatic interaction, so as to stabilize the complex. Replacement of the N -sulfate by an N -acetyl group also eliminates the specific calcium-binding capability of heparin.