High-performance liquid chromatography of amino acids, peptides and proteins. LXXXV. Separation of isoforms of the glycoprotein hormones from human pituitary extracts

Procedures for the high-resolution separation of microheterogeneous forms of the glycoprotein hormones, lutropin, follitropin and thyrotropin, present in human pituitary extracts are described. The sequential use of preparative isoelectric focusing and ion-exchange high-performance liquid chromatography (HPLC) allows the further discrimination of the isoforms of these glycoprotein hormones, previously considered homogeneous on the basis of their electrophoretic mobility. The ability of ion-exchange HPLC stationary phases to probe for slight differences in charge asymmetry expressed on the surface of these proteins raises the possibility of their rapid purification via the tandem on-line use of the same ion-exchange support with several different elution systems. Retention maps, illustrating the basis of this approach, are described.