The detection of four molecular forms of human transferrin during the iron binding process

Abstract Human transferrin has been separated into four molecular forms by electrophoresis in a medium containing 6 M urea and a Tris/borate/EDTA, pH 8.4, buffer. The separation of these forms correlates directly with the amount of iron bound by the transferrin: iron free transferrin, iron bound only to site A of transferrin, iron bound only to site B of transferrin and iron bound to both iron binding sites of transferrin. The molecular basis for the electrophoretic separation of human transferrin into four molecular forms is complex and incompletely defined at this time. However, this separation appears to be related to two phenomena observed in this work and by other investigators: (1) the increase in protein stability as iron is bound to transferrin and (2) the assymetrical distribution of amino acids in the transferrin molecule. Whatever the exact reason, the observed phenomenon has potential use in further evaluation of both the physicochemical and physiological processes in which transferrin participates.