Download Human Catalase Enzyme and more Study notes Biochemistry in PDF only on Docsity! NAME: SANDIPAN SAHA IIT MADRAS BIO-INORGANIC CHEMISTRY 1 | P a g e CATALASE • Human catalase is a heme-containing peroxisomal enzyme that breaks down hydrogen peroxide produced as a byproduct of metabolism, to water and oxygen. The reaction occurs in two stages: • Catalase is a tetramer of four polypeptide chains, each over 500 amino acids long. It contains four iron-containing heme groups that allow the enzyme to react with hydrogen peroxide. • Catalase protects hemoglobin by removing over half of the hydrogen peroxide generated in normal human erythrocytes, which are exposed to substantial oxygen concentrations. It can break down approximately one million molecules of hydrogen peroxide per second. • Without catalase hydrogen peroxide would build up and cause damage to the cell and could even signal it to initiate cell death, leading to the human genetic disease known as acatalasemia, or Takahara's disease. PRIMARY & SECONDARY STRUCTURE: • Human Catalase is a tetrameric protein of 244 kDa containing 1997 amino acid residues in a total of four identical subunits (named A, B, C, D) of 59.7 kDa. • The alpha helices and beta-sheets formed are indicated alongside. NAME: SANDIPAN SAHA IIT MADRAS BIO-INORGANIC CHEMISTRY 2 | P a g e TERTIARY STRUCTURE: • Human catalase forms a tetramer composed of four subunits, each of which can be conceptually divided into four domains. The extensive hydrophobic core of each subunit is generated by an eight-stranded antiparallel β-barrel (β1-8), with nearest neighbor connectivity capped by β-barrel loops on one side and α9 on the other. • The β-barrel is comprised of two four-stranded sheets with residues from Met339 to Ala345 and the end of β2’ wedged between β4 and β5. The N-terminal threading arm (residues 5- 70) intricately connects two subunits by hooking through a long wrapping loop (residues 380-438) around another subunit. • Finally, a helical domain at one face of the β-barrel is composed of four C-terminal helices (α16, α 17, α 18, and α19) and four helices derived from residues between β4 and β5 (α4, α5, α6, and α7). QUATERNARY STRUCTURE: DIMER & TETRAMER: Dimeric Structure (Catalase) Tetrameric Structure(Catalase) ◦ Two arm-exchanged dimers, which are related by the Q-axis of the P,Q,R molecular axes, assemble to form the 222-symmetric tetramer which is roughly square with overall dimensions 100 Aº ,100 Aº ,70 Aº. ◦ Tetramerization forces the N-terminal threading arms from the arm-exchanged dimer to cover the heme active site for the other pair of dimers (related by the R-axis) and suggests
