The calcium-dependent electrophoretic shift of α-lactalbumin, the modifier protein of galactosyl transferase

α-Lactalbumin, the modifier protein of galactosyl transferase in the synthesis of lactose by the mammary gland, has been shown to undergo a Ca 2+-dependent electrophoretic shift. Such shifts, characteristic of most calcium modulated proteins, are related to gross conformational changes upon binding calcium when detected in the presence of detergent (SDS-PAGE). However, we detected the calcium shift for α-lactalbumin using non-denaturing PAGE (ND-PAGE) where electrical charge changes are observed upon binding calcium. In order for a shift to be observed between the apo and calcium bound protein, calcium ion binding to proteins must have minimal dissociation constants (K diss) of 10 −7 M; α-lactalbumin is reported to bind calcium at K diss = 10 −10 to 10 −12 M. The electrophoretic shift identifies α-lactalbumin in complex milk whey patterns of many species of mammals.