The Distribution of Iron between the Metal-Binding Sites of Transferrin in Human Serum

The Makey & Seal [(1976) Biochim. Biophys. Acta 453, 250-2561 method of polyacrylamide-gel electrophoresis in buffer containing 6M-urea was used to determine the distribution of iron between the N-terminal and C-terminal iron-binding sites of transferrin in human serum. In fresh serum the two sites are unequally occupied; there is preferential occupation of the N-terminal site. On incubation of the serum at 370C the preference of iron for the N-terminal site becomes more marked. On storage of serum at -150C the iron distribution changes so that there is a marked preference for the Cterminal site. Dialysis of serum against buffer at pH 7.4 also causes iron to be bound much more strongly by the C-terminal than by the N-terminal site. The original preference for the N-terminal site can be restored to the dialysed serum by addition of the diffusible fraction.