Three-dimensional structure of the enzyme catalase

Abstract

Catalase (H₂O₂ : H₂O₂-oxidoreductase, EC 1.11.1.6) is an enzyme that catalyses decomposition of hydrogen peroxide to oxygen and water, and is present in all aerobic cells. All catalases studied so far are tetrameric, each subunit (molecular weight ∼60,000) being formed by a single polypeptide chain with haemin as a prosthetic group^1,2. Catalase is one of the most efficient enzymes known, resulting in reaction rates approaching the diffusion-controlled limit. Knowledge of the three-dimensional structure of catalase should help to increase our understanding of its mechanism of action, which is at present rather poor. It will also be of interest to compare the structure of catalase with that of other haem proteins, particularly from the point of view of evolutionary relationships. Thus, we have now analysed the three-dimensional structure of catalase from the fungus Penicillium vitale. From an electron density map at 3.5 Å resolution it was possible to trace the polypeptide chain. The haem group has been identified, and the active site localized using the specific inhibitor 3-amino-1:2:4-triazole. P. vitale catalase subunits have been shown to be composed of three domains, with α + β, α and α/β type secondary structures respectively. Comparison with the structure of beef liver catalase³ shows that the latter enzyme lacks the C-terminal domain of the P. vitale enzyme.