<p>O-Glycosyl hydrolases <db_xref db="EC" dbkey="3.2.1."/> are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycosyl hydrolases, based on sequence similarity, has led to the definition of 85 different families [<cite idref="PUB00004870"/>, <cite idref="PUB00005266"/>]. This classification is available on the CAZy (CArbohydrate-Active EnZymes) web site.</p>This group of beta-galactosidase enzymes (<db_xref db="EC" dbkey="3.2.1.23"/>) belong to the glycosyl hydrolase 42 family <db_xref db="CAZY" dbkey="GH42"/>. The enzyme catalyses the hydrolysis of terminal, non-reducing terminal beta-D-galactosidase residues. Glycoside hydrolase, family 42, N-terminal