ERYTHROPOIETIN AND THE INDUCTION OF ERYTHROID CYTODIFFERENTIATION. Page: 4 of 14
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Sheep plasma erythropoietin is composed of 74% protein and 26% carbohydrate.
The carbohydrate consists of 10% - 11% sialic acid (16-18 residues mole), 6%
galactose (18 residues/mole), 4% mannose (12 residues/mole), 4% glucosamine
(12 residues/mole), and 2% glucose (6 residues/mole). Microdetermination of
the amino acid composition has not yet been carried out satisfactorily, but,
within the limit of detection, there appears to be no 'methionine or cysteine
(less than.2-3 residues/mole) and only small amounts of arginine, tyrosine and
valine. The absorbance maximum in the middle ultraviolet range is 276 nm and
the A1% at that wavelength is 7.4.
The molecular weight of the iodinated erythropoietin determined by
electrophoresis in gels containing sodium dodecyl sulfate (Weber and Osborn,
1969) is 46000. (Goldwasser and Kung, 1972).
The effects of chemical and enzymic probes, of known specificities, on
the biological activity of erythropoietin can give us some information about
the chemical nature of the hormone. A requirement for tyrosine or histidine
was deduced from the inactivation by fluoroscein isothiocyanate (Lowy and
Borsook, 1962) and-by iodination (Goldwasser and Kung, unpublished); that of
arginine or lysine, from the inactivation by trypsin. Treatment of erythro-
poetin with hydroxynitrobenzylbromide, which is specific for tryptophan, also
caused loss of activity (Lowy and Keighly, 1968). Reaction with p-chloro-
mercuribenzoate, on the other hand, did not inactivate, nor did esterification
of primary alochol groups with anhydrous formic acid (Lowy, Keighly and
We have found that removal of the terminal sialic acids by either acid
or sialidase treatment causes complete loss .of activity whether the in vivo
assay is done in fasted rats or plethoric mice. When the assay was done in
vitro, no loss of activity could be detected. Speculations about this seeming
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Goldwasser, E. ERYTHROPOIETIN AND THE INDUCTION OF ERYTHROID CYTODIFFERENTIATION., report, January 1, 1972; Country unknown/Code not available. (digital.library.unt.edu/ark:/67531/metadc1031224/m1/4/: accessed January 20, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.