Biochemical characterization of an in-vitro murine megakaryocyte growth activity: megakaryocyte potentiator.

The biochemical properties of an in-vitro megakaryocyte growth factor called megakaryocyte potentiator (Mk-POT) were investigated. P388D1 cell conditioned medium (P388D1 CM), was used as the source of Mk-POT. The potentiator activity had an apparent mol. wt of 21 kilodaltons (kd) by gel filtration and was eluted from DEAE-Sepharose pH 8.0 with 0.15 M NaCl. Chromatofocusing revealed three active species with apparent pIs of 4.0, 5.5 and above 6.0. Most Mk-POT activity does not bind to Concanavalin A-Sepharose. Mk-POT activity is sensitive to reduction by dithiothreitol and temperatures above 90 degrees C. Treatment with trypsin, alpha-chymotrypsin and pronase also reduced the Mk-POT activity, but it was not destroyed by RNase A or neuraminidase. It is precipitated in ammonium sulphate solutions of between 60 to 70% saturation, and by 80% ethanol. The Mk-POT activity is stable in solutions of pH 5.0-9.0. The data presented here suggest that megakaryocyte potentiator is either heterogeneous in its properties or more than one molecular species may express the in-vitro Mk-POT activity found in P388D1 CM.