Catalase is a key enzyme in the metabolism of H2O2 and reactive oxygen species (ROS), and its expression and localization is markedly altered in tumors[1]. Free oxygen radical scavenger.

Catalase, the enzyme that metabolizes H2O2 but also reacts with a multitude of other substrates. The active site of catalase contains an iron atom. Human catalase contains four identical subunits, each subunit containing four distinct domains and one prosthetic heme group. The four domains include: (1) a N-terminal arm which contains a distal histidine, an essential amino acid for the catalase reaction; (2) a β-barrel domain that contains eight β-barrels arranged in an antiparallel fashion with six α-helical insertions, conferring the hydrophobic core of the protein necessary for the tri-dimensional structure of the enzyme; (3) a connection domain which contains the tyrosine residue that binds the heme group; and finally (4) an α-helical domains, which is important for NADPH binding[1].

References:
[1]. Glorieux C, et al. Catalase, a remarkable enzyme: targeting the oldest antioxidant enzyme to find a new cancer treatment approach. Biol Chem. 2017 Sep 26;398(10):1095-1108.