Two apparent molecular forms of bovine lactoferrin

Bovine lactoferrin was prepared by CM-Sephadex column chromatography from defatted colostrum. When partially purified lactoferrin was analyzed by SDS-PAGE apparently two polypeptides of different size appeared. The polypeptides were transferred to a nitrocellulose sheet and visualized using antirabbit serum raised against the small polypeptide. Two polypeptides appeared clearly when stained by an immunological method. The color intensity of the two polypeptides was similar when the polypeptides were stained with Coomassie Brilliant Blue R-250. A high similarity of cyanogen bromide cleavage patterns between the two polypeptides was also observed in those stained with dye and immunologically visualized. Therefore, it is suggested that these polypeptides are lactoferrins. Comparison of the peptide patterns of the two lactoferrin molecules being deglycosylated suggested that sugar moieties may be one, but not all, of the causes of the size heterogeneity in lactoferrin. These results suggest that bovine colostrum contains two lactoferrin molecules of different size, although the physiological significance of the heterogeneity is not yet known.