CALCIUM-ION BINDING OF 3 DIFFERENT TYPES OF OLIGO POLYSIALIC ACIDS ASSTUDIED BY EQUILIBRIUM DIALYSIS AND CIRCULAR DICHROIC METHODS/

Ca2+ binding properties of three different types of oligo/polysialic a cid chains, i.e., oligo/poly(Neu5Ac), oligo/poly(Neu5Gc), and oligo/po ly(KDN), were studied by equilibrium dialysis and circular dichroism. Colominic acid, high molecular weight polysialoglycoprotein (H-PSGP), low molecular weight polysialoglycoprotein (L-PSGP), and 3-deoxy-D-gly cero-D-galacto-2-nonulosonic acid (KDN) glycoprotein were found to bin d calcium ions with about 8-100 times the affinity of sialic acid mono mer. Analysis by equilibrium dialysis of the binding of Ca2+ to colomi nic acid was biphasic, and the high-affinity interaction was shown to change with the degree of polymerization. Specific binding of Ca2+ to polysialic acid (polySia) caused characteristic effects in the circula r dichroism spectrum. A pronounced decrease in the circular dichroism of polySia at 205 nm was observed upon addition of calcium. H-PSGP was found to bind calcium ions with 3-fold higher affinity than L-PSGP.