NMR Studies of the Structure and Environment of the Milk Protein α-Lactalbumin

Abstract

α-Lactalbumin (o-LA) plays a unique role in milk biochemistry. That is, its function appears to be only as a modifier protein in lactose biosynthesis by directing the specificity of galactosyl transferase from the acceptor substrate N-acetylglucosamine (GlcNAc) to glucose (Glc). Specifically, α-lactalbumin lowers the K_M for Glc from 1.4 M to 5.0 mM, while the reaction involving GlcNAc as an acceptor becomes inhibited in the presence of α-lactalbumin (Hill and Brew, 1975). Actually, it was not known until very recently that α-LA was a calcium-binding protein. It had been studied extensively in the past by Kronman and colleagues (Kronman et al., 1964; Kronman and Andreotti, 1972) yet it was never realized that the protein existed in several conformations due to multiple states of cation binding. In fact, much of the published data on the physical or structural properties of this protein previous to 1978 are ambiguous since workers were not aware that their α-LA samples contained calcium and/or other strongly bound cations.