structural studies of endonucleases have revealed a similar architecture for the active site with the residues following the weak consensus sequence glu/asp-(x)-glu/asp/ser-x-lys/glu. "bgl"ii's active site is similar to other endonucleases', following the sequence asp-(x)-glu-x-gln. in its active site there sits a divalent metal cation, most likely mg, that interacts with asp-84, val-94, a phosphoryl oxygen, and three water molecules. one of these water molecules, is able act as a nucleophile because of its proximity to the scissile phosphoryl (its orientation being fixed by a hydrogen bond with the side chain amide oxygen of gln-95) and its contact with the metal cation (which lowers its pk, promoting the water's nucleophilicity).