Evidence of human hemoglobin interaction with chorionic gonadotropin hormone: Prospects for the use of hemoglobin as ligand in affinity chromatography for the purification of the hormone

ABSTRACT

The purification of biomolecules is a necessary step in many biochemical researches. In this regard, developments of convenient, specific and low cost methods of purification are of particular interest. Given the human hemoglobin [Hb] affinity toward some charged carbohydrates, interaction of this molecule with human chorionic gonadotropin [hCG] which is a glycoprotein hormone containing sialic acid, was examined. In the current study, we gathered evidence of free hCG and free Hb interaction using spectroscopic and radiometric techniques. Then, based on the affinity of hemoglobin [Hb] toward charged carbohydrates on human chorionic gonadotropin [hCG], a known sialic acid containing glycoprotein hormone, Hb-sepharose as well as native and denatured globin columns for isolation of the hormone were prepared. Sepharose-6B was activated by cyanogens bromide. Native Hb, normal globin and denatured globin were bound to cyanogen bromide-activated sepharose. Then, uptake of hCG by these gels were compared. Among the columns only native hemoglobin-sepharose column was able to catch a limited number of serum proteins such as hCG. Using the above column hCG hormone was purified with fold purification of 34 and efficiency of 80%. The chromatographic behavior of growth hormone [GH] and hCG in binding to the DEAE-Cellulose column were identical but GH showed no binding to Hb-sepharose column, indicating that the retention mechanism of hCG to Hb-sepharose column is not a simple ion exchange mode. Since globin had no property to attach to hCG but native Hbsepharose was able to catch hCG, the BPG cavity of Hb is suggested as the possible binding site for hCG to Hb