Partial purification and biochemical characterization of human plasma thrombopoietin

A factor that stimulates the incorporation of 75Selenomethionine into the newly formed platelets of recipient mice (thrombopoietin, TPO) has been partially purified from the plasma of thrombocytopenic patients. The activity was precipitated at 60-80% ammonium sulfate saturation and further purified with hydrophobic interaction chromatography. Thrombopoietin was retained by concanavalin-A-Sepharose. Using HPLC size-exclusion chromatography, an approximate molecular weight of 40,000 dalton was calculated. The overall purification factor was about 2,100-fold. TPO was stable in a pH range from 5 to 9 and was heat-sensitive, and the biological activity was destroyed by trypsin treatment and by dithiothreitol. The partially purified molecule did not stimulate the proliferation of megakaryocyte progenitors in vitro and had no effect on the growth of erythroid or granulocyte-macrophage colonies; when administered in-vivo, TPO significantly affected the mean platelet volume and increased the number of small acetylcholinesterase cells in the bone marrow. TPO appears to be specific for the megakaryocytic lineage and active on the postmitotic compartment of megakaryocytes.