Characterization and properties of the human and bovine lactotransferrins extracted from the faeces of newborn infants.

Human lactotransferrin was characterized in the faecal extracts from breastfed babies. Quantitative determination of human copro-lactotransferrin from birth for a period of up to 3 weeks showed that the daily elimination decreased from 35 to 5 mg. The amount of copro-lactotransferrin corresponding to the endogenous secretion was calculated to be from 0.5 to 1 mg per day. When a cow's milk diet supplemented by partially or completely iron-saturated human or bovine lactotransferrin was fed to the babies, the amounts of copro-lactotransferrin excreted depended on the origin and on the iron saturation of the lactoransferrin. In particular, the amount of bovine copro-lactotransferrin in the faeces averaged 200 mg per day. The human and bovine copro-lactotransferrins were isolated by ion-exchange chromatography or by affinity chromatography and were still able to bind iron. The fingerprints of native human and bovine lactotransferrins hydrolysed in vitro by infant's gastric or duodenal secretions showed that both proteins were not extensively digested. This demonstrates that these lactotransferrins ingested by babies are not completely destroyed and keep their ability to bind iron, and thus may supplement the bacteriostatic effects of the endogenous lactotransferrin in the intestinal tract.