Hooked on alpha-D-galactosidases: from biomedicine to enzymatic synthesis

?-d-Galactosidases (EC 3.2.1.22) are enzymes employed in a number of useful bio-based applications. We have depicted a comprehensive general survey of ?-d-galactosidases from different origin with special emphasis on marine example(s). The structures of natural ?-galactosyl containing compounds are described. In addition to 3D structures and mechanisms of action of ?-d-galactosidases, different sources, natural function and genetic regulation are also covered. Finally, hydrolytic and synthetic exploitations as free or immobilized biocatalysts are reviewed. Interest in the synthetic aspects during the next years is anticipated for access to important small molecules by green technology with an emphasis on alternative selectivity of this class of enzymes from different sources.