α-Lactalbumin is a key whey protein found abundantly in cow’s milk and the milk of many other mammals. In primates, its expression is regulated by the hormone prolactin, which stimulates the synthesis of α-lactalbumin during lactation to boost lactose production. Functionally, α-lactalbumin serves as the regulatory subunit of the lactose synthase enzyme complex, partnering with β-1,4-galactosyltransferase (beta4Gal-T1), the catalytic subunit. This partnership dramatically increases the enzyme’s affinity for glucose-by approximately 1000-fold-enabling efficient transfer of galactose to glucose and resulting in lactose synthesis, which is essential for milk production.