Purification and characterization of the mouse thymocyte Thy-1 glycoprotein

The thymocyte Thy-1 glycoprotein was purified from mouse strain NMRI (Thy 1.2) thymus. Crude membranes were prepared in Tween 20 and solubilized in deoxycholate. The glycoproteins were isolated by affinity chromatography on concanavalin A-Sepharose, and Thy-1 was further purified by two gel-filtration cycles on Sephacryl S-200. The concentration of Thy-1 in fractions obtained during purification was measured by a solid-phase radioimmunoassay with pure mouse brain Thy-1 as standard. Analysis of the purified preparation by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis revealed at least five distinct bands in the apparent-Mr region 25000-30000, the polymorphism probably being due to carbohydrate heterogeneity. Amino-acid-analysis data were compatible with the previously published sequence of mouse brain Thy-1. Sugar content was determined at 31% (w/w), and the carbohydrate composition indicates the presence of 'complex-type' oligosaccharide chains. The mean Mr of mouse thymocyte Thy-1 was calculated to be 18 100.