In contrast to these studies, Panjamurthy et al. showed that activities of enzymatic antioxidants including SOD, CAT measured in plasma, erythrocytes and gingival tissues were elevated in periodontitis, whereas activities of non-enzymatic antioxidants including vitamins E, vitamin C, and reduced glutathione were decreased in periodontitis (Panjamurthy et al., 2005). Here, CAT is linked to periodontitis.