Methane monooxygenase Compound

Brazeau, B. J., and Lipscomb, J. D., 1999, Effect of temperature on the methane monooxygenase compound Q formation and decay processes, J. Inorg. Biochem. 74 8 1. 

Enzymes necessary for the metabolism of a substrate may be induced by growth on structurally unrelated compounds. In the examples used for illustration, monooxygenases play a cardinal role as a result of the versatility of methane monooxygenase, while monooxygenases that may be involved in toluene degradation are discussed in Chapter 3, Part 1 and Chapter 8, Part 1. 

In some cases, microorganisms can transform a contaminant, but they are not able to use this compound as a source of energy or carbon. This biotransformation is often called co-metabolism. In co-metabolism, the transformation of the compound is an incidental reaction catalyzed by enzymes, which are involved in the normal microbial metabolism.33 A well-known example of co-metabolism is the degradation of (TCE) by methanotrophic bacteria, a group of bacteria that use methane as their source of carbon and energy. When metabolizing methane, methanotrophs produce the enzyme methane monooxygenase, which catalyzes the oxidation of TCE and other chlorinated aliphatics under aerobic conditions.34 In addition to methane, toluene and phenol have been used as primary substrates to stimulate the aerobic co-metabolism of chlorinated solvents. 

A new class of metalloprotelns containing polynuclear, non-heme oxo-bridged iron complexes has emerged recently. Dinuclear centers are present in hemerythrin (Hr), ribonucleotide reductase (RR), purple acid phosphatases (PAP) and, possibly, methane monooxygenase (MMO) these centers as well as model compounds are reviewed in Chapter 8. 

Colby, J., D. I. Stirling, and H. Dalton, The soluble methane monooxygenase from Methylococcus copsulatus bath - Its ability to oxygenate n-alkanes, ethers and alicyclic, aromatic, and heterocyclic compounds , Biochem. J., 165, 395-402 (1977). 

Since H202 is easier to handle than 02, we will focus on the use of the former. Many metals can be used for this transformation [50]. Among them, iron compounds are of interest as mimics of naturally occurring non-heme catalysts such as methane monooxygenase (MMO) [51a] or the non-heme anti-tumor drug bleomycin [51b]. Epoxidation catalysts should meet several requirements in order to be suitable for this transformation [50]. Most importantly they must activate the oxidant without formation of radicals as this would lead to Fenton-type chemistry and catalyst decomposition. Instead, heterolytic cleavage of the 0—0 bond is desired. In some cases, alkene oxidation furnishes not only epoxides but also diols. The latter transformation will be the topic of the following section. 

Chan, S. I., Nguyen, H.-H. T., Shiemke, A. K., and Lidstrom, M. E., 1992, Biochemical and biophysical studies toward characterization of the membrane-associated methane monooxygenase. 7th Intern. Symp. on Microbial Growth on Cl Compounds. J. C. Murrell, and D. P. Kelly. Andover UK, Intercept Ltd., 93nl07. 

Rataj, M. J., Kauth, J. E., and Donnelly, M. L, 1991, Oxidation of deuterated compounds by high specific activity methane monooxygenase from Methylosinus trichosporium. Mechanistic implications, J. Biol. Chem. 266 18684918690. 

During the ferroxidation reaction, a blue color with an absorption maximum of 650 run appears. This persists in oxygen-limited conditions and decays as iron oxidation proceeds. " In frog H-chain ferritin, resonance Raman studies indicate a similar absorption is associated with an Fe(III)-tyrosinate. Harrison and Treffty have considered these and other studies and attribute the transient color to formation of a /x-l,2-peroxodiferric intermediate, which decays to a more stable /x-oxodiferric species as occurs in methane monooxygenase, ribonucleotide reductase, and model compounds. Protein radicals distinct from reactive oxygen species have been observed that have been attributed to damage caused by Fenton chemistry. ... 

Figure 19 Best present model for compound Q of methane monooxygenase.

Various iron salts and mononuclear Fe or binuclear Fe complexes with a N,0 environment, biomimetic to methane monooxygenase complexes, have been applied to the oxidation of cyclohexane with various oxidants [6u,v,7a-g], but their catalytic activity is usually modest, with the exception of a hexanuclear Fe(III) compound derived from p-nitrobenzoic acid, which gives the highest total yield to Ol/One of about 30% [7a]. Moreover, most of these complexes are often unstable and very expensive. A hexanuclear heterotrimetallic Fe/Cu/Co complex bearing two Cu(p-0)2Co(p-0)2Fe cores, prepared by self-assembly, oxidizes cyclohexane with aqueous HP, with a maximum yield to Ol/One of 45%, virtually total selectivity to the two compounds, and preferred formation of cyclohexanol [7hj. The remarkable activity of the Fe/Cu/Co cluster was associated with the synergic effect of the three metals. 

---