Purification and Properties of Human Transferrin C and a Slow Moving Genetic Variant

Human transferrin C and a genetic variant found by a starch gel electrophoresis screening program were purified and compared structurally. Isolation combined two bulk fractionations, with the use of rivanol and ammonium sulfate, with the more selective procedures of Sephadex G-100 gel filtration and diethylaminoethyl Sephadex A-50 ion exchange chromatography. Transferrin C and the variant were separated during the latter. The product obtained was homogeneous in the ultracentrifuge (s20,w = 5.1 S), in free boundary electrophoresis at several pH values (mobility = -3.03 and -3.63 units for apo- and ferritransferrins C, respectively, in pH 8.6 Veronal; isoelectric point, pI, of apotransferrin C = 5.5), in immunoelectrophoresis, and in starch gel electrophoresis. Amino acid analyses agreed with published data but failed to reveal differences between the two varieties. The peptide map of the Caucasian variant D-G.F. contains all the peptide spots seen in the map from transferrin C and a single additional spot not seen in the latter. The peptide is neutral at pH 6.5 and fails to stain for arginine, histidine, or tyrosine. This variant peptide is assumed to arise from one of two overlapping peptides, from the unresolved core, or from a peptide produced from two distinct parts of the molecule.