Quantitative adsorption of platelet glycoprotein G (thrombin-sensitive protein, thrombospondin) to barium citrate

Glycoprotein G (thrombin-sensitive protein, thrombospondin) is a high-Mr calcium-sensitive protein secreted by activated platelets. We observed that this protein was precipitated with barium citrate, and this property was used to purify glycoprotein G. The simple and rapid purification procedure consisted of barium citrate adsorption followed by heparin-agarose affinity chromatography. Unlike other calcium-sensitive proteins that are precipitated by barium citrate, glycoprotein G does not contain gamma-carboxyglutamic acid. The ability of glycoprotein G to bind to both heparin and barium citrate is consistent with this protein possessing clusters of positive and negative charges.