lactose synthase activity

Definition

Target type: molecularfunction

Catalysis of the reaction: UDP-galactose + D-glucose = UDP + lactose. [EC:2.4.1.22]

Lactose synthase, also known as lactase-phlorizin hydrolase (LPH), is a key enzyme responsible for the synthesis of lactose, the primary sugar found in mammalian milk. The enzyme is a complex of two proteins: alpha-lactalbumin (α-LA) and galactosyltransferase (β4GalT1). β4GalT1 alone possesses the enzymatic activity to transfer galactose from UDP-galactose to N-acetylglucosamine, forming the precursor for glycoproteins. However, the presence of α-LA dramatically alters the specificity of β4GalT1, allowing it to transfer galactose to glucose instead, resulting in the formation of lactose. This change in specificity is achieved through a conformational change induced by α-LA binding to β4GalT1, creating a binding site for glucose. The reaction catalyzed by lactose synthase proceeds in two steps: first, β4GalT1 transfers galactose from UDP-galactose to glucose, forming lactose. Second, UDP is released, and the lactose synthase complex dissociates. The overall activity of lactose synthase is tightly regulated by various factors, including hormones, nutritional status, and developmental stage. The activity is highest during lactation, ensuring the production of sufficient lactose for milk production. The molecular function of lactose synthase activity is therefore crucial for the synthesis of lactose, which serves as the primary energy source for newborn mammals.'
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Proteins (1)

Compounds (1)