Abstract
Summary
Cohn fractions of normal human plasma were surveyed for erythropoietin activity by an in vivo and two in vitro assay systems. Fractions II + III, II + III W, and especially fraction III, were found to stimulate glucosamine incorporation and heme synthesis of marrow cells in culture. Log dose-log response regression lines of plasma fractions and of an erythropoietin standard were found to be parallel. Only traces of activity could be detected by the exhypoxic polycythemic mouse assay. Fraction III from several different sources and species was found to be active in vitro. A human fraction III was shown to have a different specific activity relative to a common erythropoietin standard in the two in vitro assays. Subfractionation of fraction III by extraction procedures demonstrated low stability for the activity measured by the 59Fe-heme assay, whereas it was possible to obtain without loss a preparation enriched in the activity stimulating glucosamine incorporation.
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