IUBMB Enzyme Nomenclature


Accepted name: lactase

Reaction: lactose + H2O = β-D-galactose + D-glucose

Glossary: lactose = β-D-galactopyranosyl-(1→4)-α-D-glucopyranose

Other name(s): lactase-phlorizin hydrolase; LPH (gene name); LCT (gene name)

Systematic name: lactose galactohydrolase (configuration-retaining)

Comments: The enzyme from intestinal mucosa contains two glycosyl hydrolase domains, both of which belong to glycosyl hydrolase family 1 (GH1). While the first domain catalyses the activity described here, the second domain catalyses the reaction of EC glycosylceramidase. cf. EC amylo-α-1,6-glucosidase.

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 9031-11-2


1. Asp, N.G., Dahlqvist, A. and Koldovský, O. Human small-intestinal β-galactosidases. Separation and characterization of one lactase and one hetero β-galactosidase. Biochem. J. 114 (1969) 351-359. [PMID: 5822067]

2. Schlegel-Haueter, S., Hore, P., Kerry, K.R. and Semenza, G. The preparation of lactase and glucoamylase of rat small intestine. Biochim. Biophys. Acta 258 (1972) 506-519. [PMID: 5010299]

3. Lorenz-Meyer, H., Blum, A.L., Haemmerli, H.P. and Semenza, G. A second enzyme defect in acquired lactase deficiency: lack of small-intestinal phlorizin-hydrolase. Eur. J. Clin. Invest. 2 (1972) 326-331. [PMID: 5082068]

4. Ramaswamay, S. and Radhakrishnan, A.N. Lactase-phlorizin hydrolase complex from monkey small intestine. Purification, properties and evidence for two catalytic sites. Biochim. Biophys. Acta 403 (1975) 446-455. [PMID: 810166]

5. Skovbjerg, H., Sjöström, H. and Norén, O. Purification and characterization of amphiphilic lactase-phlorizin hydrolase from human small-intestine. Eur. J. Biochem. 114 (1981) 653-661. [PMID: 6786877]

6. Skovbjerg, H., Norén, O., Sjöström, H., Danielsen, E.M. and Enevoldsen, B.S. Further characterization of intestinal lactase/phlorizin hydrolase. Biochim. Biophys. Acta 707 (1982) 89-97. [PMID: 6814489]

7. Zecca, L., Mesonero, J.E., Stutz, A., Poiree, J.C., Giudicelli, J., Cursio, R., Gloor, S.M. and Semenza, G. Intestinal lactase-phlorizin hydrolase (LPH): the two catalytic sites; the role of the pancreas in pro-LPH maturation. FEBS Lett. 435 (1998) 225-228. [PMID: 9762914]

8. Arribas, J.C., Herrero, A.G., Martin-Lomas, M., Canada, F.J., He, S. and Withers, S.G. Differential mechanism-based labeling and unequivocal activity assignment of the two active sites of intestinal lactase/phlorizin hydrolase. Eur. J. Biochem. 267 (2000) 6996-7005. [PMID: 11106409]

[EC created 1984, modified 2022]

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