Manganese catalase mechanism

Fig. 14 Proposed mechanism for disproportionation of H2O2 by manganese catalase (reprinted with permission from Ref 107, Copyright 2004 American Chemical Society).

The importance of reactions 1-3 in the biosphere is clear. However, relatively little is known about the catalytic mechanisms of these reactions, particularly reactions 2 and 3. In order to better understand the catalytic mechanisms of these enzymes, it is important to establish the correlation between metal site structure and enzymatic function. X-ray absorption spectroscopy is one of the premier tools for determining the local structural environment of metalloprotein metal sites. In the following, we summarize our results using X-ray absorption spectroscopy to characterize the structure of the Mn active site environments in manganese catalase and in the OEC and show how these structural results can be used to deduce details of the catalytic mechanism of these enzymes. 

Scheme 8. A proposed mechanism for the disproportionation of hydrogen peroxide by manganese catalase, based on the mechanism proposed by Penner-Hahn in 1992, and the T. thermophilus catalase crystal structure. [Adapted with permission from (24). Copyright 1992 WILEY-VCH Verlag.]...

Fig. 5. Proposed mechanism for H2O2 decomposition by manganese catalase (5).

Sakiyama explored various dinuclear manganese complexes as catalase mimics derived from 2,6-bis N-[(2-dimethylamino)ethyl]iminomethyl-4-methylphenolate (2, Figure 10.1) and related ligands. Employing UV- ds and MS techniques both mono-and di-Mn -oxo intermediates could be detected [30]. Notably, the proposed mechanism (Scheme 10.2) is different from that reported for the manganese catalases and model compounds containing ligand 1 [30]. 

Research conducted at Washington State University, as well as in situ applications by commercial entities, has indicated that stabilization of hydrogen peroxide is necessary for effective subsurface injection [39]. Without stabilization, added peroxide decomposes rapidly through interaction with iron oxyhydroxides, manganese oxyhydroxides, dissolved metals, and enzymes (e.g., peroxidase and catalase). Some of these peroxide decay pathways involve nonhydroxyl radical-forming mechanisms, and therefore are especially detrimental to Fenton oxidation systems. 

Figure 10 Proposed mechanism of action for the enzyme catalase involving mixed valence states of manganese. (Ref 28. Reproduced by permission of Kluwer Academic Publishers)...

Alkyl hydroperoxides, manganese, ribonucleotide reductose, hydrogen peroxide, catalase activity, tetranuclear manganese, PSII, OEC, cumene, cumene hydroperoxide, biomimetic catalysis, bioinspired catalysis, C-H activation (hydrogen activation), oxygen activation, hydroperoxide decomposition, radicals (alkyl radicals and hydroperoxy radicals) and hydrogen rebound (rebound mechanisms). 

Biochemically, manganese is considered an essential trace element, participating in a number of hiomolecules superoxide dismutase (Mn-SOD), catalase, Mn-ribonucleotide reductase, Mn-peroxidase, ligninase, the o>ygen-evolving centre (OEC) of photosystem ii (PS-ii), and Mn-thiosulfate oxidase. The enzymes mechanisms are very diverse and include oxo-atom transfer (four-electron oxidation of water to diojygen in PS-ii, extradiol dioxygenase), electron transfer (SOD, catalase), reduction of ribonucleotides to water and deoxyribonucleotides and oxidation of thiosulfate to sulfate. ... 

The Sq -> S2 reaction involves 0x0 (hydroxo) bridge formation between Mn ions. The PSII manganese cluster also exhibits a catalase activity. It vigorously disprOTortionates added H2O2 in the dark following formation of the So state by a single flash. The mechanism involves initial 2e" reduction S2 ->Sq with O2 formation followed by reoxidation to the So state with H2O release fScheme IV This reaction does not occur if Mn is removed or if me Mn cluster is destroyed. 

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