The most significant residue in the enzymatic activity, however, is Asp-295. Upon cleavage of the fructofuranosyl from sucrose, the resultant glucose forms a covalent intermediate with the enzyme. The carboxylate side chain of Asp-295 hydrogen bonds with the hydroxyl groups at C-2 and C-3 of the glucosyl residue. This interaction is maximized during the transition state of this covalent complex, lending support to the ping-pong mechanism. Finally, phosphorylation of the glucosyl residue at C-1 forms a transient positive charge on the glucosyl carbon, promoting breakage of the ester bond between Asp-192 and the sugar residue. Cleavage yields the product, α-D-glucose-1-phosphate.