<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><p>Glycoside hydrolase family 27 <db_xref db="CAZY" dbkey="GH27"/> comprises enzymes with several known activities; alpha-galactosidase (<db_xref db="EC" dbkey="3.2.1.22"/>); alpha-N-acetylgalactosaminidase (<db_xref db="EC" dbkey="3.2.1.49"/>); isomalto-dextranase (<db_xref db="EC" dbkey="3.2.1.94"/>).</p><p> Alpha-galactosidase (melibiase) catalyses the hydrolysis of melibiose into galactose and glucose [<cite idref="PUB00005652"/>]. In man, deficiency in the enzyme results in Fabry's disease (X-linked sphingolipidosis). Alpha-N-acetylgalactosaminidase catalyses the hydrolysis of terminal non-reducing N-acetyl-D-galactosamine residues in N-acetyl-alpha-D-galactosaminides [<cite idref="PUB00002595"/>]. Two conserved Asp residues may be involved in the catalytic mechanism in these enzymes. Deficiency in this enzyme results in Schindler and Kanzaki diseases.</p>