Galactoside

[1] Depending on whether the glycosidic bond lies "above" or "below" the plane of the galactose molecule, galactosides are classified as α-galactosides or β-galactosides.

A β-galactoside is a type of galactoside in which the glycosidic bond lies above the plane of the galactose residue.

[citation needed] However, other chemicals, such as ONPG, are known, but these are typically synthesized for biochemical assays.

Galactosides play significant roles in metabolic processes of many organisms and are hydrolyzed by a class of enzymes called galactosidases and are classified according to what type of glycosidic linkage on the galactoside they will break.

[2] For example, enzymes that hydrolyze the β-galactoside glycosidic bond are called β-galactosidases, while those that hydrolyze the α-galactoside glycosidic bond are known as α-galactosidases.