The optimum temperature for human<unk>  is about 37 °C and the optimum pH is 6. In metabolism, the β-glycosidic bond in D-lactose is hydrolyzed to form D-galactose and D-glucose, which can be absorbed through the intestinal walls and into the bloodstream. The overall reaction that<unk>  catalyzes is C12H22O11 + H2O → C6H12O6 + C6H12O6 + heat. The catalytic mechanism of D-lactose hydrolysis retains the substrate anomeric configuration in the products. While the details of the mechanism are uncertain, the stereochemical retention is achieved off a double displacement reaction. Studies of E. coli<unk>  have proposed that hydrolysis is initiated when a glutamate nucleophile on the enzyme attacks from the axial side of the galactosyl carbon in the β-glycosidic bond. The removal of the D-glucose leaving group may be facilitated by Mg-dependent acid catalysis. The enzyme is liberated from the α-galactosyl moiety upon equatorial nucleophilic attack by water, which produces D-galactose. Substrate modification studies have demonstrated that the 3′-OH and 2′-OH moieties on the galactopyranose ring are essential for enzymatic recognition and hydrolysis. The 3′-hydroxy group is involved in initial binding to the substrate while the 2′- group is not necessary for recognition but needed in subsequent steps. This is demonstrated by the fact that a 2-deoxy analog is an effective competitive inhibitor (Ki = 10mM). Elimination of specific hydroxyl groups on the glucopyranose moiety does not eliminate catalysis. Proposed mechanism of<unk>  hydrolysis by<unk>  enzyme<unk>  also catalyzes the conversion of phlorizin to phloretin and glucose.
Lactase
Alpha-amylase
Amidase
Wobenzym
Fibrinolysin
Proteases 
Pancreatic elastase
Iduronidase