A Cortisol-induced Charge Difference in Desialylated Human Transcortin Detected by Isoelectric Focusing

Abstract

Abstract Human desialylated transcortin was found to be microheterogeneous by isoelectric focusing. All samples tested showed two cortisol-binding components. Liganded with cortisol these components are isoelectric at pH 5.2 and 5.4. In the unliganded form, however, they eluted at pH 5.4 and 5.6, respectively. This cortisol-controlled transition was reversible in both directions. Isolated components containing trace amounts of [3H]cortisol accumulate the steroid in the position of the corresponding liganded form at the anodic side of the unliganded binder. Electrofocusing of desialylated plasma containing [3H]cortisol results in a cortisol accumulation at pH 5.1 at the anodic side of the unliganded binding components. The experiments show that electrofocusing can profitably be used to study ligand-protein interactions and that radioligand detection is not always an adequate method to localize a macromolecular binding agent.