Marked stereoselectivity in the binding of copper ions by heparin. Contrasts with the binding of gadolinium and calcium ions.

Heparin forms a complex with cupric ion (Cu2+) at a level of less than or equal to 10(-3) mol of the metal ion per dimeric unit of the polymer, as evidenced by paramagnetic relaxation effects on its 1H- and 13C-n.m.r. spectra. No interaction occurred with heparin derivatives modified either by desulfation of the residues of alpha-L-iduronic acid 2-sulfate, or by hydrolysis of the sulfamino group of the residues of 2-deoxy-2-sulfamino-alpha-D-glucose 6-sulfate, although binding was induced by N-acetylation of the latter derivative. Under the same experimental conditions, no alternative type of glycosyluronic acid structure tested, including the other glycosaminoglycans, showed significant relaxation enhancement by Cu2+. These results are in contrast to those obtained with gadolinium ion (Gd3+), another paramagnetic probe, or with calcium ion (Ca2+), which promotes chemical-shift displacements. The binding selectivities of those two cations are much broader than that of Cu2%, although they also differ notably in their relationship to the structure of heparin.