Hematin iron valence in catalase and peroxidase compound I: Relationship to free radical reaction mechanism

• Published in: Free radical biology & medicine Vol. 5; no. 2; pp. 89 - 93
• Main Authors: Dounce, Alexander L., Sichak, S.Paul
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 1988; Elsevier Science
• Subjects: Analytical, structural and metabolic biochemistry; Biological and medical sciences; Catalase; Catalase - metabolism; Chemical Phenomena; Chemistry; Enzyme mechanisms; Enzymes and enzyme inhibitors; Free Radicals; Fundamental and applied biological sciences. Psychology; Hematin iron valence; Heme - metabolism; Horseradish Peroxidase - metabolism; Hydride ion transfer; Iron - metabolism; Oxidoreductases; Peroxidase; Peroxidases - metabolism; π cation radical; Hematin iron valence; Enzyme mechanisms; Peroxidase; Catalase; π cation radical; Hydride ion transfer; Reaction mechanism; Iron; Enzyme; Free radical
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/0891-5849(88)90034-2

The material in this paper is centered on the structure of compound I (first reaction intermediate) in the case of catalase and a classical peroxidase (horseradish peroxide, HRP). The concept of a π-cation radical is accepted for HRP but is rejected in the case of catalase. A possible mechanism for catalatic action previously proposed assumes FeV for the hematin iron of catalase and hydride ion transfer in the reduction of FeV by the second molecule of H 2O 2, no free radical being involved. In the case of HRP however, FeIV is assumed for compound I. A hypothetical ·OH needed to balance the reaction for the formation of compound I is thought to interact with the π electron cloud of the hematin prosthetic group, forming the now generally accepted π cation radical and an OH − ion. Attempts to apply the π cation mechanism to catalatic action lead to contradictions and implausible chemical reactions.