Internal β(1-4) galactose linkages in unbranched, repeating poly-Nacetyllactosamine [GlcNAc β(1-3)Gal β (1-4)] structures are the preferred substrate.Sulfated structures such as keratan sulfate are also cleaved. Branching and/or fucosylation of the substrate may reduce or completely inhibit cleavage. Sulfation of C-6 on galactose will block cleavage. Oligosaccharides of the neolacto-group are cleaved at greatly reduced rates depending on the deviation from the preferred substrate. For example, Gal β(1-3)GlcNAc β(1-3) Gal β(1-4)Glc is cleaved at 5X10-5 the rate of keratan sulfateβ-galactosidase cleaves lactose into its monosaccharide components, glucose and galactose. It also catalyses the transglycosylation of glucose into allolactose, the inducer of β-galactosidase, in a feedback loop.
