The role of α-lactalbumin in lactose synthetase

Abstract

The A protein of lactose synthetase can catalyze lactose formation from UDP-galactose and glucose even in the absence of α-lactalbumin but only poorly because of a very high K m for glucose. α-Lactalbumin decreases the K m for glucose as well as that for N-acetylglucosamine (NAG). Depending only on the substrate concentration α-lactalbumin can stimulate disaccharide formation or inhibit this process both with NAG and with glucose. The affinities of the two sugars are such that under normal assay conditions, in the presence of α-lactalbumin, the concentration of glucose is optimal for lactose synthesis whereas that of NAG is inhibitory.