Bovine galactosyltransferase: interaction with alpha-lactalbumin and the role of alpha-lactalbumin in lactose synthase.

Bovine alpha-lactalbumin has been dansylated to give an enzymatically fully active, highly fluorescent derivative. This derivative is uniquely labeled on the N-terminal glutamic acid residue of alpha-lactalbumin. This fluorescent derivative of alpha-lactalbumin has been covalently cross-linked to galacto-syltransferase by using dimethyl pimelimidate. Resonance energy transfer measurements using cobalt bound to the transferase as the acceptor of energy transfer from the dansyl group on the alpha-lactalbumin indicate that the dansyl group is 32 A from the cobalt of the transferase. A model of the active site of the transferase and its interaction with alpha-lactalbumin is proposed on the basis of these and previous studies.