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Erythropoietin is a prime regulator of human red blood cell differentiation. Both the kidney and the liver are involved in Epo production. The kidney is the major site of Epo production in adults and the liver is involved in extrarenal Epo production. Under anemic or anoxic: stress, both the production and excretion of this hormone increase considerably. Epo is an acidic glycoprotein which contains 166 amino acids. It has a molecular weight of 34,000-39,000 and a pI of 4.1. Many attempts have been made to purify human Epo. It has been purified to homogeneity using size and charge separation techniques, a combination of hydro-phobic interaction and immunoaffinity chromatography, or immunochemical purifications with monoclonal anti-body or site-specific antibody. Epo is known to stimulate proliferation as well as differentiation of normal erythroid progenitors. However, little is known of Epo´s mechanism of action. The receptors of Epo have been identified recently in the Friend virus-infected erythroid cells. As an initial event after binding the receptor. Epo rapidly alters protein phosphorylation in the membranes of erythroids cells. This effect appears to be relevant to the hormone´s biological action.
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