SOD1 and cystic fibrosis: This interenzymatic activity imbalance was accentuated with replicative senescence: the SOD/GPx ratio was 2.3-fold higher in T21F than in CF at HP, the SOD/CAT ratio 2.6 times higher in T21F than in CF at HP, and the SOD/(GPx+CAT) 2.4-fold higher in T21F than in CF at HP.