-galactosidase can catalyze three different reactions in organisms. In one, it can go through a process called transgalactosylation to make allolactose, creating a positive feedback loop for the production of β-gal. Allolactose can also be cleaved to form monosaccharides. It can also hydrolyze lactose into galactose and glucose which will proceed into glycolysis. The active site of β-galactosidase catalyzes the hydrolysis of its disaccharide substrate via "shallow" (nonproductive site) and "deep" (productive site) binding. Galactosides such as PETG and IPTG will bind in the shallow site when the enzyme is in "open" conformation while transition state analogs such as L-ribose and D-galactonolactone will bind in the deep site when the conformation is "closed".