Catalase is an enzyme that not only metabolizes H2O2 but also interacts with various other substrates. Its active site includes an iron atom. Human catalase consists of four identical subunits, with each subunit comprising four distinct domains and a single prosthetic heme group. The four domains are: (1) a N-terminal arm featuring a distal histidine, a crucial amino acid for the catalase reaction; (2) a β-barrel domain with eight β-barrels in an antiparallel arrangement and six α-helical insertions, which create the protein’s hydrophobic core essential for its three-dimensional structure; (3) a connection domain that includes the tyrosine residue binding to the heme group; and (4) an α-helical domain important for NADPH binding^[1].