Purification of Platelet Glycocalicin and Glycoprotein I by Affinity Techniques

Glycocalicin and glycoprotein I are similar, or identical, proteins which appear to differ in their degree of affinity for the platelet surface and which mediate the interaction of thrombin and Factor VIII with platelets. Glycocalicin has now been purified from the soluble fraction of platelet homogenate by a two step procedure involving affinity chromatography on WGA-Sepharose and elution with borate-glucosamine, followed by affinity chromatography on thrombin-Sepharose and elution with heparin or 1 M sodium chloride. Glycoprotein I was prepared from a Triton extract of platelet membranes by a similar series of steps, but in this case two fractions were obtained requiring elution from WGA-Sepharose by borate-glucosamine alone or in the presence of deoxycholate. However, the borate-glucosamine eluate separated again into two fractions on rechromatography on WGA-Sepharose. The final product was less soluble than glycocalicin itself. Cyanogen bromide fragmentation of glycocalicin gave one Pas-positive band, a major band and three minor CBB bands. These studies suggest that glycocalicin and glycoprotein I may show functional and structural dissimilarities. (Supported, in part, by USPHS Grants Nos. HL14697 and HL20971.)