XDH and Hypertension: However, under pathological conditions such as ischemia-reperfusion, inflammation and hypertension XDH can be reversibly or irreversibly converted to the oxidase form of the enzyme (XO) via oxidation of cysteine residues (Cys535, Cys992) or proteolytic cleavage of lysine (Lys 551, Lys 569) respectively [1,2].