Occurs in almost all aerobically respiring organisms and serves to protect cells from the toxic effects of hydrogen peroxide. 2 H2O2 = 2 H2O + O2 Homotetramer. In stems, leaves, roots and developing fruits. In roots, by aluminum and salt. Expressed with a circadian rhythm reaching a maximum at late in the dark period or early in the light period. Belongs to the catalase family.