A sensitive and convenient assay procedure for transferrin and its application to the purification of mouse transferrin.

A sensitive procedure employing 55Fe binding was developed for the assay of transferrin. This procedure took advantage of the pH dependence and reversibility of iron binding by transferrin and was applicable to both human and mouse transferrins. Excess iron, after saturation of the transferrin iron-binding sites with 55Fe, supplied as Fe-citrate, was efficiently removed by its binding to Amberlite CG-400 anion-exchange resin. Mouse transferrin was purified from plasma using a combination of ammonium sulphate fractionation and ion-exchange chromatography. Two peaks of pure transferrin were obtained by DEAE-Sepharose chromatography. Mouse transferrin was found to have a molecular weight of 80 000.