title: Multinuclear magnetic resonance studies of the interaction of inorganic cations with heparin.
abstract: The interaction of Na+, Ca2+, Mg2+, Zn2+ and La3+ with heparin, a highly negatively charged glycosaminoglycan, was studied by 1H and 23Na nuclear magnetic resonance spectroscopy. 1H chemical shift and nuclear Overhauser effect (NOE) data indicate that the counter ions Na+, Ca2+ and Mg2+ interact with the low pH, carboxylic acid form of heparin by delocalized, long-range electrostatic interactions. At higher pH, 1H chemical shift and NOE data indicate that Na+ and Mg2+ continue to interact with heparin in the same manner, even upon deprotonation of the carboxylic acid group; however, there is a site-specific contribution to the binding of Ca2+, Zn2+ and La3+ under these conditions. Acid dissociation constants for heparin carboxylic acid groups and heparin-metal binding constants were determined from the pH dependence of 1H chemical shifts and 23Na spin-lattice (T1) relaxation times. Equilibrium constants for exchange of M2+ for heparin-bound Na+ were obtained from 23Na T1 data. The acid dissociation constants show a strong dependence on Na+ concentration due to the polyelectrolyte character of heparin.
authors.affiliation: Department of Chemistry, University of California, Riverside 92521, USA.
authors.forename: D L
authors.initials: DL
authors.lastname: Rabenstein
authors.forename: J M
authors.initials: JM
authors.lastname: Robert
authors.forename: J
authors.initials: J
authors.lastname: Peng
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002264:Carboxylic Acids / Q000378:metabolism; D002412:Cations / Q000378:metabolism*; D002417:Cattle; D006493:Heparin / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000737:chemistry; D008168:Lung / Q000737:chemistry; D008274:Magnesium / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D012964:Sodium / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism; D017186:Titrimetry
chemical_list: D002264:Carboxylic Acids; D002412:Cations; D013431:Sulfates; D006493:Heparin; D012964:Sodium; D008274:Magnesium; D002118:Calcium