Characterization of murine erythropoietin

Although erythropoietins from human and sheep sources have been purified, a mouse erythropoietin remains essentially uncharacterized despite the fact that the mouse is most commonly used to assay for erythropoietin. Because other murine growth factors may have erythropoietic activity it will be essential to compare these with erythropoietin from murine sources rather than from other species. Here we compare the physicochemical properties and some of the bioactivities of erythropoietins from anemic mouse serum and human urine in parallel fractionations. Both molecules showed similar molecular weights (40-45,000) by gel filtration and similar retention characteristics on reverse-phase high-performance columns. However, they differed in their relative solubility in ammonium sulfate, hydrophobicity on phenyl-Sepharose, and in their ability to bind to a phenyl-boronate agarose column. Despite these differences the two molecules stimulated the same number of CFU-E in the mouse fetal liver assay and did so with similar dose-response relationships. The data indicate that putative murine erythropoietic stimuli must be compared with murine erythropoietin and not human urine erythropoietin before concluding, on the basis of fractionation results, that a factor is different from erythropoietin.