CAT and idiopathic pulmonary fibrosis: Furthermore, IPF is associated with an increased oxidant burden and diminished expression of antioxidant enzymes, including heme oxygenase-1 (HO-1), superoxide dismutase (SOD), catalase (CAT), glutaredoxin and glutamate cysteine synthase (γGCS, the rate-limiting enzyme in glutathione synthesis) [5,6], which is thought to further enhance epithelial injury.