Essential residues in the active site of vanadium haloperoxidases include: Lys353, Arg360, Arg490, His404, and His496. Corresponding residues in the active site of glucose 6-phosphatase-α include Arg170 and Arg83, which donate hydrogen ions to the phosphate, stabilizing the transition state, His119, which provides a proton to the dephosphorylated oxygen attached to glucose, and His176, which completes a nucleophilic attack on the phosphate to form a covalently bound phosphoryl enzyme intermediate. Within the Vanadium-containing chloroperoxidase, Lys353 was found to stabilize the phosphate in the transition state. However, the corresponding residue in glucose 6-phosphatase-α (Lys76) resides within the ER membrane and its function, if any, is currently undetermined. With the exception of Lys76, these residues are all located on the luminal side of the ER membrane.