α-galactosidase (EC 3.2.1.22) (melibiase) [1] catalyzes the hydrolysis of melibiose into galactose and glucose. In man, the deficiency of this enzyme is the cause of Fabry's disease (X-linked sphingolipidosis). α-galactosidase is present in a variety of organisms. There is a considerable degree of similarity in the sequence of α-galactosidase from various eukaryotic species.

Escherichia coli α-galactosidase (gene melA), which requires NAD and magnesium as cofactors, is not structurally related to the eukaryotic enzymes; by contrast, an Escherichia coli plasmid encoded α-galactosidase (gene rafA) [2] contains a region of about 50 amino acids which is similar to a domain of the eukaryotic α-galactosidases.

α-N-acetylgalactosaminidase (EC 3.2.1.49) [3] catalyzes the hydrolysis of terminal non-reducing N-acetyl-D-galactosamine residues in N-acetyl-α-D-galactosaminides. In man, the deficiency of this enzyme is the cause of Schindler and Kanzaki diseases. The sequence of this enzyme is highly related to that of the eukaryotic α-galactosidases.

We selected, as a signature pattern for these enzymes, the N-terminal part of the conserved domain. The pattern contains two conserved aspartic acid residues which could be involved in the catalytic mechanism.