Nutritional and physiologic significance of alpha-lactalbumin in infants.

alpha-Lactalbumin is the major protein in breast milk (20-25% of total protein) and has been described to have several physiologic functions in the neonatal period. In the mammary gland, it participates in lactose synthesis, thereby creating an osmotic "drag" to facilitate milk production and secretion. alpha-Lactalbumin binds divalent cations (Ca, Zn) and may facilitate the absorption of essential minerals, and it provides a well-balanced supply of essential amino acids to the growing infant. During its digestion, peptides appear to be transiently formed that have antibacterial and immunostimulatory properties, thereby possibly aiding in the protection against infection. A novel folding variant ("molten globule state") of multimeric alpha-lactalbumin has recently been discovered that has anti-infective activity and enhances apoptosis, thus possibly affecting mucosal cell turnover and proliferation. Cow milk also contains alpha-lactalbumin, albeit less than human milk (2-5% of total protein in bovine milk), and protein fractions enriched with alpha-lactalbumin may now be added to infant formula to provide some of the benefits of human alpha-lactalbumin.