Physiochemical properties of erythropoietin: Isoelectric focusing and molecular weight studies

Abstract

In this study, ESF has been further characterized with respect to isoelectric point and molecular weight. Isoelectric points varied widely for human urinary ESF, ranging from pH 4.1 to 5.8. Sheep plasma ESF had a relatively low pI, which agreed with published results, but rabbit plasma ESF had a significantly higher pI. It was concluded that ESF is a heterogeneous macromolecule, both between human patients and between species. The molecular weights of ESF from human urine and rabbit and sheep plasma were determined by PAGE and by gel filtration in 6 m GuHCl. Molecular weights determined in polyacrylamide gels were consistently higher (51,300 ± 6,000 daltons) than those obtained by gel filtration (33,000 ± 2,900 daltons). Since glycoproteins frequently appear to have higher molecular weights in polyacrylamide gels, it was concluded that the average value obtained by gel filtration of 33,000 daltons was the more accurate value. Since other laboratories have found the molecular weight of ESF to be approximately twice the value by gel filtration in the presence of 6 m GuHCl, the molecular weights of ESF reported here are for the monomeric form of ESF; however, ESF exists as a dimer in nature.