Structural studies on individual components of bovine transferrin

Abstract

The single banding components of bovine transferrin from animals homozygous for the four transferrin variants found in the U.K. were isolated. Sedimentation equilibrium ultracentrifugation and sodium dodecylsulphate polyacrylamide gel electrophoresis showed that the bands of a single variant have molecular weights of 77500 and 73300, respectively. The different bands of a single variant and single bands of different variants show no evidence of size heterogeneity or of low molecular weight peptides being split off after reduction in 6M guanidine hydrochloride. The two slower bands of a single variant, which both contain 2 molecules of sialic acid/molecule of protein, have the same molecular weight and amino acid composition, and give identical peptide 'maps', although differences in composition and peptide 'maps' occur between the different variants. The results support the concept that bovine transferrin is essentially a single polypeptide chain, but they do not explain differences in electrophoretic mobility between bands of the same variant which are not produced by differing sialic acid content.