Isolation of two biologically active peptides, erythrotropin I and erythrotropin II from fetal calf intestine.

A bioassay based on the measurement of thymidine incorporation into trichloroacetic acid-insoluble materials in erythroid cell suspensions from fetal calf liver was used as the assay for purification of two small peptides (erythrotropins I and II) from fetal calf intestine. The peptides were purified using reversed-phase and gel permeation high performance liquid chromatography (HPLC). The two peptides have very similar amino acid compositions and a molecular weight of about 3500 daltons. Erythrotropin II stimulated thymidine incorporation and potentiated the action of erythropoietin in cultures of erythroid cells from fetal rat liver.