Isolation of the two monoferric human transferrins by preparative isoelectric focussing.

1. Human transferrin was labelled with Fe(III) in nitrilo triacetate buffer at one of its two metal binding sites by variation of the pH. The A-site was preferentially labelled at pH 7.2, the B-site at pH 9.2. 2. The monoferric transferrin preparations were subjected to preparative isoelectric focussing, isolated from the granulated gels, and checked for homogeneity and purity on an analytical scale by isoelectric focussing. 3. The technique for obtaining stable monoferric transferrin (Fe)(A) and transferrin (Fe)(B) preparations is described in detail.